AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
137 PM PDT FRI MAR 23 2007
.SYNOPSIS...
AN UPPER LEVEL LOW WILL CONTINUE TO MOVE EAST ACROSS SONORA MEXICO
TONIGHT. A HIGH PRESSURE RIDGE WILL BUILD OVER SOUTHERN CALIFORNIA
THROUGH THE WEEKEND. A COASTAL EDDY WILL DEVELOP TONIGHT AND BE
PRESENT DURING THE NIGHT AND MORNING HOURS THROUGH SUNDAY. ON MONDAY
THE HIGH PRESSURE RIDGE WILL BREAK DOWN. ON TUESDAY A STORM SYSTEM
MOVING INLAND TO THE NORTH. THIS WILL BRING GUSTY WINDS...COOLER
TEMPERATURES...AND A CHANCE OF RAIN AND MOUNTAIN SNOW TO SOUTHERN
CALIFORNIA. FAIR WEATHER AND A SLOW WARMING TREND ARE EXPECTED FOR
THE LATTER HALF OF NEXT WEEK AS HIGH PRESSURE REBUILDS.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM (TONIGHT THROUGH MONDAY)...
LOW MOVING OFF TO THE EAST AND SUBSIDENCE ALOFT FROM RIDGE BUILDING
IN HAS CAPPED CONVECTION OVER SOUTHWEST CALIFORNIA.
OVER CONVECTION. LEFT A MENTION OF SHOWERS OVER THE EAST SLOPES FOR
THIS EVENING BUT CHANCE OF MEASURABLE AMOUNTS ARE PRETTY SLIM.
SOUTHERLY WINDS AT COASTAL STATIONS SUPPORT EDDY DEVELOPMENT AND
NAM12 MODEL INDICATES IT WILL PRESENT DURING THE NIGHT AND MORNING
HOURS WITH ONSHORE FLOW IN THE AFTERNOONS. THE RIDGE ALOFT WILL BE
BUILDING AT THE SAME TIME AND THE 1000-500 MB THICKNESS INCREASES
SUPPORT ABOUT 3 TO 5 DEGREES WARMING EACH DAY...BUT DO NOT EXPECT TO
SEE ANY WARMING OVER INLAND VALLEYS AND LIKELY COOLING OVER COASTAL
SECTIONS DUE TO INCREASE IN STRATUS. ON MONDAY THE RIDGE IS
FLATTENED AS LONG WAVE TROUGH ADVANCES TOWARDS COAST. THIS SHOULD
BRING THICKENING AND LOWERING CIRROSTRATUS CLOUDS AND LIFTING OF THE
STRATUS CLOUDS TO THE LOWER COASTAL SLOPES...RESULTING IN A GENERAL
COOL DOWN FOR ALL AREAS.
&&
.LONG TERM (TUESDAY THROUGH FRIDAY)...
FOR TUESDAY THE TROUGH MOVES INLAND TO THE NORTH. MAIN EFFECT ON
SOUTHERN CALIFORNIA EXPECTED TO BE STRONG GUSTY WINDS...ABOUT 20
DEGREES COOLING...AND A SLIGHT CHANCE OF RAIN AND MOUNTAIN SNOW.
HAVE SNOW LEVEL LOWERING TO 4000-4500 FEET ON TUESDAY. FOR WEDNESDAY
HIGH PRESSURE REBUILDS BUT REGION STILL IN COOL NORTHWEST FLOW. FOR
THURSDAY AND BEYOND THE MEDIUM RANGE MODELS GO OUT OF PHASE. WILL
STAY WITH SCENARIO OF WEAK HIGH PRESSURE REBUILDING THROUGH
FRIDAY...FOR SLOW WARM UP BACK TO SEASONAL TEMPERATURES.
&&
.AVIATION...
231900Z...LATE MORNING ACARS SOUNDINGS INDICATE THE MARINE LAYER
DEPTH NEAR KSAN WAS AROUND 1000 FEET. A MODERATE COASTAL EDDY OVER
THE COASTAL WATERS WILL HELP MAINTAIN THE MARINE LAYER THROUGH
SATURDAY. AN AREA OF STRATUS ALONG THE SOUTHERN ORANGE COUNTY AND
NORTHERN SAN DIEGO COUNTY COASTLINE SHOULD EXPAND THIS EVENING AND
PUSH INLAND. BASES OF THE STRATUS SHOULD BE AROUND 800 FEET MSL SO
AS THE STRATUS PUSHES INLAND...EXPECT IFR CEILINGS AT MOST COASTAL
AIRPORTS TONIGHT WITH LIFR CEILINGS POSSIBLE AT SOME OF THE MESA AND
INLAND VALLEY AIRPORTS. STRATUS SHOULD STAY AWAY FROM THE KONT AREA
BUT SOME RADIATIONAL FOG MAY DEVELOP IN THE VICINITY OF
KONT...ESPECIALLY AROUND KCNO BEFORE SUNRISE ON SATURDAY.
ABOVE THE MARINE LAYER...MID AND HIGH LEVEL WRAP AROUND MOISTURE
SHOULD CONTINUE TO DIMINISH THROUGH TONIGHT AS THE UPPER LOW CURRENT
OVER NORTHWEST SONORA IN MEXICO CONTINUES TO DRIFT SLOWLY TO THE
EAST. BASES SHOULD REMAIN ABOVE 12000 FEET MSL.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&
$$
PUBLIC/FIRE WEATHER...BALFOUR
AVIATION/MARINE.......HORTON
NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS TAUNTON MA
1025 PM EDT SAT MAR 24 2007
.UPDATE...
RAIN HAS MIXED WITH OR CHANGED TO SNOW MOST PLACES NORTH AND EAST OF
A WINDSOR LOCKS-WILLIMANTIC LINE...MEANWHILE THE BACK EDGE OF PRECIP
ON THE ALY RADAR IS MOVING INTO THE BERKSHIRES IN THE SOUTH AND WILL
REACH THE GREEN MOUNTAINS IN THE NORTH...AND SHOULD MOVE EAST OF
MASSACHUSETTS BY 06Z WITH A FEW WIDELY SCATTERED SNOW SHOWERS
POSSIBLE AFTER THE MAIN AREA MOVES EAST. HAVE ADJUSTED THE FORECAST
TO THIS TIMING AND REMOVED FURTHER MENTION OF SLEET. ASIDE FROM
PRECIP TIMING AND COOLING TEMPS A COUPLE OF DEGREES...NO MAJOR
CHANGES PLANNED IN THE FORECAST.
&&
.PREV DISCUSSION...
/ISSUED 809 PM EDT SAT MAR 24 2007/
UPDATE...
KBOX RADAR SHOWING 40+ DBZ OVER NORTHERN CONNECTICUT. CROSS SECTIONS
SHOW THESE 40+ DBZ ALL AROUND AND BELOW 10 THOUSAND FEET WITH 20 DBZ
BELOW 20 THOUSAND FEET. BDL REPORTED 0.12 RAINFALL BETWEEN 7 AND 8
PM. AMDAR AIRCRAFT DESCENT SOUNDING INTO BDL AT 7 PM SHOWED AN
ISOTHERMAL LAYER AROUND 0C FROM 3000 FEET TO 10000 FEET. AT THE
MOMENT THIS LAST SENTENCE WAS BEING WRITTEN...TWO REPORTS OF SLEET
CAME IN FROM HARTFORD AND ATTLEBORO. WILL AMEND FORECAST TO INCLUDE
OCCASIONAL SLEET FOR AREAS SOUTH OF THE MASS PIKE WHERE THE HIGHER
DBZ ARE SHOWING. NO OTHER CHANGES AT THIS MOMENT.
PREV DISCUSSION...
/ISSUED 450 PM EDT SAT MAR 24 2007/
.STILL EXPECTING A 2 TO 5 INCH SNOWFALL ACROSS INTERIOR TONIGHT
WITH GREATEST AMOUNTS IN HIGHER ELEVATIONS...
SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
CLOUD SHIELD CONTINUES TO MAKE STEADY EASTWARD PROGRESS AND WILL
OVERSPREAD SOUTHERN NEW ENGLAND BY EARLY EVENING. RADAR MOSAIC HAS
LEADING EDGE OF SHOWERS INTO NORTHERN NY AND EVEN ADJACENT PARTS OF
NORTHERN NEW ENGLAND...BUT MOST OF THIS IS ALOFT. RAIN IS REACHING
GROUND FARTHER W NEAR WATERTOWN AND SYRACUSE.
WE ARE CONTINUING SNOW ADVISORY FOR TONIGHT...BUT WE HAVE NUDGED
TOTALS UP SLIGHTLY OVER INTERIOR NE MA WHICH MEANS WE WILL ADD
CENTRAL MIDDLESEX COUNTY MA TO ADVISORY AT THIS TIME.
12Z NAM/GFS ARE IN GENERAL AGREEMENT IN HANDLING OF POTENT SHORT
WAVE AND ASSOCIATED SURFACE LOW DIVING SE FROM GREAT LAKES TONIGHT.
WE ARE LEANING MORE TOWARD NAM FOR DETAILS GIVEN ITS BETTER
RESOLUTION SINCE ELEVATION WILL PLAY A LARGE ROLE IN RAIN VS SNOW AS
WELL AS SNOWFALL TOTALS.
WE DO THINK NAM IS A BIT OVERDONE WITH ITS QPF OF 0.50 TO 0.75 INCH
ACROSS MUCH OF NORTHERN MA AND SW NH...ESPECIALLY WHEN COMPARED WITH
09Z SREFS WHICH ONLY SUPPORT 0.25 TO 0.50 INCH. HOWEVER THEY DO
AGREE THAT AXIS OF MAX QPF WILL BE ACROSS OUR NORTHERN ZONES...WITH
LESSER AMOUNTS OF 0.10 TO 0.25 INCH S OF MASS PIKE.
WE HAVE WARMED UP NICELY THIS AFTERNOON WITH ALL LOCATIONS WELL UP
INTO THE 40S AND LOWER 50S. IT IS THIS LOW LEVEL WARMING THAT WILL
BE KEY PLAYER IN HOW FAST WE SEE A CHANGEOVER FROM RAIN TO
SNOW...SINCE ALOFT IT IS STILL FAIRLY COLD AND WILL EASILY SUPPORT
SNOW AT ONSET. THIS IS A TYPICAL SPRING SNOWFALL EVENT WHERE HIGHER
ELEVATIONS ARE FAVORED...BUT SINCE SNOW WILL BE FALLING AT NIGHT WE
STAND TO SEE SOME ACCUMULATION AT LOWER ELEVATIONS AS WELL.
IN ORDER TO SEE MORE WIDESPREAD ADVISORY TOTALS...WE WOULD LIKE TO
SEE STRONGER LIFT ARRIVING AFTER MIDNIGHT...BUT SINCE IT IS COMING
IN DURING FIRST PART OF NIGHT...THAT SHOULD LIMIT EXTENT OF 2 TO 4
INCH TOTALS.
AS A RESULT...WE EXPECT LIGHT RAIN TO MOVE INTO SOUTHERN NEW ENGLAND
THIS EVENING...POSSIBLY MORE OF A RAIN/SNOW MIX AT HIGHER
ELEVATIONS... BEFORE CHANGING TO SNOW WITHIN A FEW HOURS OF ONSET.
IN ADDITION TO WET BULB COOLING...WE ALSO HAVE STRONG LIFT ENTERING
PICTURE AS A RESULT OF APPROACHING MID LEVEL SHORT WAVE...WHICH WILL
ALSO ACT TO COOL DOWN COLUMN FAIRLY QUICKLY. THIS CHANGEOVER WILL
TAKE PLACE BY 9 OR 10 PM ACROSS SW NH AND WESTERN/CENTRAL MA...BUT
PROBABLY NOT UNTIL 11 PM OR MIDNIGHT FARTHER S AND E INTO NORTHERN
CT...NORTHERN RI AND EASTERN MA...AND MORE LIKE 1 TO 2 AM NEAR S
COAST.
ALTHOUGH THIS SYSTEM IS PROGRESSIVE AND WILL EXIT REGION QUICKLY...
THERE WILL BE A 3 TO 4 HOUR PERIOD WHERE EVERYTHING COMES TOGETHER
TO PRODUCE DECENT SNOWFALL RATES...ESPECIALLY AT HIGHER ELEVATIONS
WHERE SNOW WILL BE MORE PROLONGED AND OVER OUR NORTHERN ZONES WHERE
CROSS SECTIONS INDICATE MAX SNOW GROWTH ZONE WILL BE. WHILE WE DO
NOT SEE SNOWFALL TOTALS IN EXCESS OF 6 INCHES IN OUR HIGHER
ELEVATION SITES...WE SHOULD BE ABLE TO GET WIDESPREAD 3 TO 5 INCH
TOTALS FROM MONADNOCKS TO E SLOPES OF BERKSHIRES AND WORCESTER HILLS
WITH 2 TO 4 INCHES ELSEWHERE ACROSS INTERIOR.
FARTHER S INTO NORTHERN CT...NORTHERN RI AND INTERIOR EASTERN MA...
WE THINK INITIAL LOW LEVEL WARMING WILL PLAY MORE OF A ROLE AND
LIMIT SNOWFALL ACCUMULATIONS TO 1 TO 3 INCHES...MAINLY ON
GRASS...SINCE RAIN/SNOW MIX SHOULD LAST A BIT LONGER AND BEST LIFT
IS CENTERED IN WARMER AIR. SOME OF HIGHER ELEVATIONS OF
HARTFORD...TOLLAND...WINDHAM AND PROVIDENCE COUNTIES COULD SEE AS
MUCH AS 3 TO 4 INCHES LOCALLY...BUT WE DO NOT THINK THESE TOTALS
WILL BE WIDESPREAD ENOUGH TO JUSTIFY ADVISORIES AT THIS TIME.
SYSTEM WILL ALREADY BE OFFSHORE SUN MORNING...SO SNOW SHOULD BE OVER
4 TO 6 AM SUN. LOW LEVEL MOISTURE WILL HANG ON INTO MORNING PER
CROSS SECTIONS...BEFORE DRYING SETS IN DURING MIDDAY AND AFTERNOON
AND ALLOWS FOR SKIES TO CLEAR.
TEMPERATURES SHOULD RECOVER NICELY SUN AFTERNOON...WELL INTO 40S IF
NOT 50F AT A FEW SPOTS S OF MASS PIKE.
WEAK HIGH PRESSURE BUILDS INTO REGION SUN NIGHT WITH ONLY PATCHY
HIGH CLOUDS EXPECTED.
LONG TERM /MONDAY THROUGH SATURDAY/...
MEDIUM RANGE MODELS SHOWED PRETTY GOOD CONTINUITY THIS AFTERNOON...
AT LEAST THE GFS SUITE AND BOTH THE GFS AND ECMWF ENSEMBLES.
ALSO...BEYOND THURSDAY...MODELS SHOWING MORE SPREAD AMONG MANY OF
THE SUITE MEMBERS...SO NOT A LOT OF CONFIDENCE WITH NEXT APPROACHING
SYSTEM OUT OF THE MIDWEST LATE NEXT WEEK. USED MAINLY THE ENSEMBLES
AND 00Z GFS FOR THIS PORTION OF THE FORECAST.
HIGH PRESSURE WILL BUILD OFF THE SOUTH COAST MONDAY...HELPING SHIFT
WINDS AROUND TO SOUTHWEST. WILL PROBABLY NOT FEEL THE FULL EFFECTS
OF WARMER TEMPERATURES...BUT HIGHS IN THE 50S WILL FEEL NICE THOUGH
REMAINING CHILLY ALONG THE SOUTH COAST. WARM FRONT DEVELOPS ACROSS
THE GREAT LAKES DURING MONDAY...WITH AREA OF PRECIP QUICKLY PUSHING
EAST.
THERE WERE TIMING ISSUES THIS WARM FRONT AND A WEAK AREA OF LOW
PRESSURE THAT MAY DEVELOP ALONG WITH IT FOR THE MONDAY NIGHT-TUESDAY
TIMEFRAME. THE NAM/WRF WAS A GOOD 6-9 HOURS SLOWER THAN THE GFS RUN.
HARD TO EXPLAIN...AS THE FORECASTED UPPER FLOW ON BOTH MODELS
APPEARS IN LINE AS A WEAKENING UPPER SHORT WAVE RIDES OVER THE UPPER
LEVEL RIDGE IN THE MIDWEST. DO NOTE THAT THE GFS IS A LITTLE FASTER
AND STRONGER AS IT MOVES THROUGH. STILL A PRETTY FAST UPPER LEVEL
FLOW...WHICH ALSO HELPS EXPLAIN THE TIMING DIFFERENCES. USED A BLEND
OF THESE MODELS FOR TIMING THIS SYSTEM INTO THE REGION...AS THIS
SYSTEM WILL BE ANOTHER FAST MOVER /SIMILAR TO TONIGHTS LOW/.
LITTLE IF ANY COLD AIR TO WORK WITH...SO EXPECT THE PRECIP TO BE ALL
RAIN AS IT APPROACHES LATE MONDAY...MOVING THROUGH TUESDAY MORNING.
FORECASTED LOW MONDAY NIGHT COULD ACTUALLY RUN A FEW DEGREES ABOVE
NORMAL WITH THIS LOW WITH SOME WARM AIR ADVECTION RIDING IN.
ONCE THE LOW AND FRONT PUSH OFF THE COAST MIDDAY TUESDAY...CLOUDS
WILL SLOWLY BREAK UP WITH DAYTIME HIGHS SOARING TO AROUND 60
DEGREES. THE OFFSHORE HIGH WILL BREAK DOWN AND HEAD EAST...WHILE
ANOTHER HIGH BUILDS SOUTHEAST OUT OF CENTRAL CANADA BY WEDNESDAY
MORNING. NOT MUCH WEATHER ASSOCIATED WITH THIS...BUT DO NOTE A
SLIGHT COOLING TREND FOR THE MIDDLE OF NEXT WEEK.
ANOTHER STRONGER LOW TAKES SHAPE OVER THE ROCKIES AROUND MIDWEEK.
THE MODEL SUITE HAD A HANDLE ON THIS LOWS DEVELOPMENT...BUT HAVE A
LOT OF ISSUES WITH THE TIMING OF THE SYSTEM AS IT TREKS ACROSS THE
NORTHERN TIER FOR LATE NEXT WEEK. APPEARS THAT...FOR NOW...WILL
CONTINUE WITH DRY WEATHER BUT A SLOW COOLING TREND AS THE CANADIAN
HIGH TAKES HOLD. UPPER RIDGE BUILDS OVER THE GREAT LAKES AND
MIDWEST...WHICH MAY HOLD THE WESTERN LOW AT BAY UNTIL LATE NEXT
WEEK. CURRENT THINKING IS TO BRING IN A LOW CHANCE OF SHOWERS FOR
FRIDAY NIGHT AND NEXT SATURDAY.
AVIATION /18Z-18Z/...
CONDITIONS LOWER TO MVFR IN CT VALLEY 00Z-02Z AND ON COASTAL PLAIN
BY 04Z SUN AS PRECIPITATION SPREADS INTO REGION AHEAD OF CLIPPER LOW
DIVING SE FROM GREAT LAKES. INITIALLY MOST LOCATIONS WILL HAVE
RAIN...OR A RAIN/SNOW MIX ACROSS INTERIOR...BEFORE A TRANSITION TO
SNOW 02Z-06Z AT ALL TERMINALS. EXCEPTION IS ON CAPE COD AND ISLANDS
WHERE WE THINK IT WILL STAY AS A MIX OF RAIN AND SNOW.
ALTHOUGH MVFR WILL DOMINATE TONIGHT WE DO EXPECT A PERIOD OF IFR
OVERNIGHT...ESPECIALLY 03Z-07Z...BEFORE CONDITIONS SLOWLY IMPROVE AS
PRECIPITATION MOVES OFFSHORE.
HIGHER TERRAIN AIRPORT SUCH AS KORH SHOULD DROP TO LIFR...AS ARE
MANY OF OUR SW NH AIRPORTS INCLUDING KMHT WHERE HEAVIEST SNOWFALL IS
EXPECTED.
WINDS NOT FORECAST TO BE AN ISSUE WITH THIS SYSTEM. LIGHT OR ONSHORE
WINDS WILL BACK TO E/NE TONIGHT AND N/NE SUN...WITH SPEEDS AOB 10KT.
MVFR TO START OFF SUN...BEFORE LIFTING TO VFR AROUND MIDDAY AS SKIES
CLEAR OUT.
OUTLOOK 18Z SUN TO 12Z MON...VFR WITH MOSTLY CLEAR SKIES AND LIGHT
WINDS.
MARINE...
LOCAL SEA BREEZES WILL GIVE WAY TO E/NE WINDS TONIGHT...BUT AOB 10KT
ON ALL WATERS. RAIN WILL MOVE INTO REGION THIS EVENING...AND WILL
CHANGE TO SNOW LATER TONIGHT BEFORE ENDING BY DAYBREAK SUN.
NE FLOW TRIES TO STRENGTHEN ON S COASTAL WATERS SUN MORNING AS LOW
PRESSURE PASSES OFFSHORE...BUT WE EXPECT WINDS AND SEAS TO REMAIN
BELOW SMALL CRAFT ADVISORY LEVELS. WEAK HIGH PRESSURE BUILDS OVER
WATERS SUN AND SUN NIGHT.
IN THE LONG TERM...HIGH PRESSURE IN CONTROL ON MONDAY...THOUGH
SOUTHWEST WINDS WILL GUST UP TO 20 KTS LATE IN THE DAY AND MONDAY
NIGHT AS WEAK LOW PRESSURE AND FRONT APPROACH. WINDS WILL SLOWLY
SHIFT TO WEST AND NORTHWEST DURING TUESDAY AS LOW CLEARS THE COAST.
HIGH PRESSURE TAKES OVER FROM CENTRAL CANADA FOR WEDNESDAY AND
THURSDAY...WITH A NORTH TO NORTHWEST FLOW. WILL KEEP WIND GUSTS UP
TO 20 KTS. BUT NOT IMPRESSIVE COLD AIR ADVECTION NOR GOOD PRESSURE
GRADIENT AT THIS POINT SO WILL KEEP BELOW SMALL CRAFT...AT LEAST ON
THE WINDS.
WNA WAVEWATCH III MODEL TRIES TO BRING SEAS UP TO NEAR OR ABOVE 5
FEET ON THE FLOW AHEAD OF THE LOW AND FRONT MONDAY THROUGH TUESDAY
NIGHT. WENT ABOUT 1 OR 2 FEET BELOW GUIDANCE. FELT THEY WERE
OVERDONE WITH THE SOUTHWEST FLOW...BUT STILL CLOSE TO OR ABOVE SMALL
CRAFT CRITERIA FOR A TIME...UPWARDS TO 6 FEET ON THE OUTER WATERS
BOTH AHEAD AND BEHIND THE LOW AND FRONT.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...SNOW ADVISORY UNTIL 4 AM EDT SUNDAY FOR MAZ002>005-008>010-012-
026.
NH...SNOW ADVISORY UNTIL 4 AM EDT SUNDAY FOR NHZ011-015.
RI...NONE.
MARINE...NONE.
&&
$$
UPDATE...
AREA FORECAST DISCUSSION
NWS TAUNTON MA
809 PM EDT SAT MAR 24 2007
.UPDATE...
KBOX RADAR SHOWING 40+ DBZ OVER NORTHERN CONNECTICUT. CROSS SECTIONS
SHOW THESE 40+ DBZ ALL AROUND AND BELOW 10 THOUSAND FEET WITH 20 DBZ
BELOW 20 THOUSAND FEET. BDL REPORTED 0.12 RAINFALL BETWEEN 7 AND 8
PM. AMDAR AIRCRAFT DESCENT SOUNDING INTO BDL AT 7 PM SHOWED AN
ISOTHERMAL LAYER AROUND 0C FROM 3000 FEET TO 10000 FEET. AT THE
MOMENT THIS LAST SENTENCE WAS BEING WRITTEN...TWO REPORTS OF SLEET
CAME IN FROM HARTFORD AND ATTLEBORO. WILL AMEND FORECAST TO INCLUDE
OCCASIONAL SLEET FOR AREAS SOUTH OF THE MASS PIKE WHERE THE HIGHER
DBZ ARE SHOWING. NO OTHER CHANGES AT THIS MOMENT.
&&
.PREV DISCUSSION...
/ISSUED 450 PM EDT SAT MAR 24 2007/
..STILL EXPECTING A 2 TO 5 INCH SNOWFALL ACROSS INTERIOR TONIGHT
WITH GREATEST AMOUNTS IN HIGHER ELEVATIONS...
SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
CLOUD SHIELD CONTINUES TO MAKE STEADY EASTWARD PROGRESS AND WILL
OVERSPREAD SOUTHERN NEW ENGLAND BY EARLY EVENING. RADAR MOSAIC HAS
LEADING EDGE OF SHOWERS INTO NORTHERN NY AND EVEN ADJACENT PARTS OF
NORTHERN NEW ENGLAND...BUT MOST OF THIS IS ALOFT. RAIN IS REACHING
GROUND FARTHER W NEAR WATERTOWN AND SYRACUSE.
WE ARE CONTINUING SNOW ADVISORY FOR TONIGHT...BUT WE HAVE NUDGED
TOTALS UP SLIGHTLY OVER INTERIOR NE MA WHICH MEANS WE WILL ADD
CENTRAL MIDDLESEX COUNTY MA TO ADVISORY AT THIS TIME.
12Z NAM/GFS ARE IN GENERAL AGREEMENT IN HANDLING OF POTENT SHORT
WAVE AND ASSOCIATED SURFACE LOW DIVING SE FROM GREAT LAKES TONIGHT.
WE ARE LEANING MORE TOWARD NAM FOR DETAILS GIVEN ITS BETTER
RESOLUTION SINCE ELEVATION WILL PLAY A LARGE ROLE IN RAIN VS SNOW AS
WELL AS SNOWFALL TOTALS.
WE DO THINK NAM IS A BIT OVERDONE WITH ITS QPF OF 0.50 TO 0.75 INCH
ACROSS MUCH OF NORTHERN MA AND SW NH...ESPECIALLY WHEN COMPARED WITH
09Z SREFS WHICH ONLY SUPPORT 0.25 TO 0.50 INCH. HOWEVER THEY DO
AGREE THAT AXIS OF MAX QPF WILL BE ACROSS OUR NORTHERN ZONES...WITH
LESSER AMOUNTS OF 0.10 TO 0.25 INCH S OF MASS PIKE.
WE HAVE WARMED UP NICELY THIS AFTERNOON WITH ALL LOCATIONS WELL UP
INTO THE 40S AND LOWER 50S. IT IS THIS LOW LEVEL WARMING THAT WILL
BE KEY PLAYER IN HOW FAST WE SEE A CHANGEOVER FROM RAIN TO
SNOW...SINCE ALOFT IT IS STILL FAIRLY COLD AND WILL EASILY SUPPORT
SNOW AT ONSET. THIS IS A TYPICAL SPRING SNOWFALL EVENT WHERE HIGHER
ELEVATIONS ARE FAVORED...BUT SINCE SNOW WILL BE FALLING AT NIGHT WE
STAND TO SEE SOME ACCUMULATION AT LOWER ELEVATIONS AS WELL.
IN ORDER TO SEE MORE WIDESPREAD ADVISORY TOTALS...WE WOULD LIKE TO
SEE STRONGER LIFT ARRIVING AFTER MIDNIGHT...BUT SINCE IT IS COMING
IN DURING FIRST PART OF NIGHT...THAT SHOULD LIMIT EXTENT OF 2 TO 4
INCH TOTALS.
AS A RESULT...WE EXPECT LIGHT RAIN TO MOVE INTO SOUTHERN NEW ENGLAND
THIS EVENING...POSSIBLY MORE OF A RAIN/SNOW MIX AT HIGHER
ELEVATIONS... BEFORE CHANGING TO SNOW WITHIN A FEW HOURS OF ONSET.
IN ADDITION TO WET BULB COOLING...WE ALSO HAVE STRONG LIFT ENTERING
PICTURE AS A RESULT OF APPROACHING MID LEVEL SHORT WAVE...WHICH WILL
ALSO ACT TO COOL DOWN COLUMN FAIRLY QUICKLY. THIS CHANGEOVER WILL
TAKE PLACE BY 9 OR 10 PM ACROSS SW NH AND WESTERN/CENTRAL MA...BUT
PROBABLY NOT UNTIL 11 PM OR MIDNIGHT FARTHER S AND E INTO NORTHERN
CT...NORTHERN RI AND EASTERN MA...AND MORE LIKE 1 TO 2 AM NEAR S
COAST.
ALTHOUGH THIS SYSTEM IS PROGRESSIVE AND WILL EXIT REGION QUICKLY...
THERE WILL BE A 3 TO 4 HOUR PERIOD WHERE EVERYTHING COMES TOGETHER
TO PRODUCE DECENT SNOWFALL RATES...ESPECIALLY AT HIGHER ELEVATIONS
WHERE SNOW WILL BE MORE PROLONGED AND OVER OUR NORTHERN ZONES WHERE
CROSS SECTIONS INDICATE MAX SNOW GROWTH ZONE WILL BE. WHILE WE DO
NOT SEE SNOWFALL TOTALS IN EXCESS OF 6 INCHES IN OUR HIGHER
ELEVATION SITES...WE SHOULD BE ABLE TO GET WIDESPREAD 3 TO 5 INCH
TOTALS FROM MONADNOCKS TO E SLOPES OF BERKSHIRES AND WORCESTER HILLS
WITH 2 TO 4 INCHES ELSEWHERE ACROSS INTERIOR.
FARTHER S INTO NORTHERN CT...NORTHERN RI AND INTERIOR EASTERN MA...
WE THINK INITIAL LOW LEVEL WARMING WILL PLAY MORE OF A ROLE AND
LIMIT SNOWFALL ACCUMULATIONS TO 1 TO 3 INCHES...MAINLY ON
GRASS...SINCE RAIN/SNOW MIX SHOULD LAST A BIT LONGER AND BEST LIFT
IS CENTERED IN WARMER AIR. SOME OF HIGHER ELEVATIONS OF
HARTFORD...TOLLAND...WINDHAM AND PROVIDENCE COUNTIES COULD SEE AS
MUCH AS 3 TO 4 INCHES LOCALLY...BUT WE DO NOT THINK THESE TOTALS
WILL BE WIDESPREAD ENOUGH TO JUSTIFY ADVISORIES AT THIS TIME.
SYSTEM WILL ALREADY BE OFFSHORE SUN MORNING...SO SNOW SHOULD BE OVER
4 TO 6 AM SUN. LOW LEVEL MOISTURE WILL HANG ON INTO MORNING PER
CROSS SECTIONS...BEFORE DRYING SETS IN DURING MIDDAY AND AFTERNOON
AND ALLOWS FOR SKIES TO CLEAR.
TEMPERATURES SHOULD RECOVER NICELY SUN AFTERNOON...WELL INTO 40S IF
NOT 50F AT A FEW SPOTS S OF MASS PIKE.
WEAK HIGH PRESSURE BUILDS INTO REGION SUN NIGHT WITH ONLY PATCHY
HIGH CLOUDS EXPECTED.
LONG TERM /MONDAY THROUGH SATURDAY/...
MEDIUM RANGE MODELS SHOWED PRETTY GOOD CONTINUITY THIS AFTERNOON...
AT LEAST THE GFS SUITE AND BOTH THE GFS AND ECMWF ENSEMBLES.
ALSO...BEYOND THURSDAY...MODELS SHOWING MORE SPREAD AMONG MANY OF
THE SUITE MEMBERS...SO NOT A LOT OF CONFIDENCE WITH NEXT APPROACHING
SYSTEM OUT OF THE MIDWEST LATE NEXT WEEK. USED MAINLY THE ENSEMBLES
AND 00Z GFS FOR THIS PORTION OF THE FORECAST.
HIGH PRESSURE WILL BUILD OFF THE SOUTH COAST MONDAY...HELPING SHIFT
WINDS AROUND TO SOUTHWEST. WILL PROBABLY NOT FEEL THE FULL EFFECTS
OF WARMER TEMPERATURES...BUT HIGHS IN THE 50S WILL FEEL NICE THOUGH
REMAINING CHILLY ALONG THE SOUTH COAST. WARM FRONT DEVELOPS ACROSS
THE GREAT LAKES DURING MONDAY...WITH AREA OF PRECIP QUICKLY PUSHING
EAST.
THERE WERE TIMING ISSUES THIS WARM FRONT AND A WEAK AREA OF LOW
PRESSURE THAT MAY DEVELOP ALONG WITH IT FOR THE MONDAY NIGHT-TUESDAY
TIMEFRAME. THE NAM/WRF WAS A GOOD 6-9 HOURS SLOWER THAN THE GFS RUN.
HARD TO EXPLAIN...AS THE FORECASTED UPPER FLOW ON BOTH MODELS
APPEARS IN LINE AS A WEAKENING UPPER SHORT WAVE RIDES OVER THE UPPER
LEVEL RIDGE IN THE MIDWEST. DO NOTE THAT THE GFS IS A LITTLE FASTER
AND STRONGER AS IT MOVES THROUGH. STILL A PRETTY FAST UPPER LEVEL
FLOW...WHICH ALSO HELPS EXPLAIN THE TIMING DIFFERENCES. USED A BLEND
OF THESE MODELS FOR TIMING THIS SYSTEM INTO THE REGION...AS THIS
SYSTEM WILL BE ANOTHER FAST MOVER /SIMILAR TO TONIGHTS LOW/.
LITTLE IF ANY COLD AIR TO WORK WITH...SO EXPECT THE PRECIP TO BE ALL
RAIN AS IT APPROACHES LATE MONDAY...MOVING THROUGH TUESDAY MORNING.
FORECASTED LOW MONDAY NIGHT COULD ACTUALLY RUN A FEW DEGREES ABOVE
NORMAL WITH THIS LOW WITH SOME WARM AIR ADVECTION RIDING IN.
ONCE THE LOW AND FRONT PUSH OFF THE COAST MIDDAY TUESDAY...CLOUDS
WILL SLOWLY BREAK UP WITH DAYTIME HIGHS SOARING TO AROUND 60
DEGREES. THE OFFSHORE HIGH WILL BREAK DOWN AND HEAD EAST...WHILE
ANOTHER HIGH BUILDS SOUTHEAST OUT OF CENTRAL CANADA BY WEDNESDAY
MORNING. NOT MUCH WEATHER ASSOCIATED WITH THIS...BUT DO NOTE A
SLIGHT COOLING TREND FOR THE MIDDLE OF NEXT WEEK.
ANOTHER STRONGER LOW TAKES SHAPE OVER THE ROCKIES AROUND MIDWEEK.
THE MODEL SUITE HAD A HANDLE ON THIS LOWS DEVELOPMENT...BUT HAVE A
LOT OF ISSUES WITH THE TIMING OF THE SYSTEM AS IT TREKS ACROSS THE
NORTHERN TIER FOR LATE NEXT WEEK. APPEARS THAT...FOR NOW...WILL
CONTINUE WITH DRY WEATHER BUT A SLOW COOLING TREND AS THE CANADIAN
HIGH TAKES HOLD. UPPER RIDGE BUILDS OVER THE GREAT LAKES AND
MIDWEST...WHICH MAY HOLD THE WESTERN LOW AT BAY UNTIL LATE NEXT
WEEK. CURRENT THINKING IS TO BRING IN A LOW CHANCE OF SHOWERS FOR
FRIDAY NIGHT AND NEXT SATURDAY.
AVIATION /18Z-18Z/...
CONDITIONS LOWER TO MVFR IN CT VALLEY 00Z-02Z AND ON COASTAL PLAIN
BY 04Z SUN AS PRECIPITATION SPREADS INTO REGION AHEAD OF CLIPPER LOW
DIVING SE FROM GREAT LAKES. INITIALLY MOST LOCATIONS WILL HAVE
RAIN...OR A RAIN/SNOW MIX ACROSS INTERIOR...BEFORE A TRANSITION TO
SNOW 02Z-06Z AT ALL TERMINALS. EXCEPTION IS ON CAPE COD AND ISLANDS
WHERE WE THINK IT WILL STAY AS A MIX OF RAIN AND SNOW.
ALTHOUGH MVFR WILL DOMINATE TONIGHT WE DO EXPECT A PERIOD OF IFR
OVERNIGHT...ESPECIALLY 03Z-07Z...BEFORE CONDITIONS SLOWLY IMPROVE AS
PRECIPITATION MOVES OFFSHORE.
HIGHER TERRAIN AIRPORT SUCH AS KORH SHOULD DROP TO LIFR...AS ARE
MANY OF OUR SW NH AIRPORTS INCLUDING KMHT WHERE HEAVIEST SNOWFALL IS
EXPECTED.
WINDS NOT FORECAST TO BE AN ISSUE WITH THIS SYSTEM. LIGHT OR ONSHORE
WINDS WILL BACK TO E/NE TONIGHT AND N/NE SUN...WITH SPEEDS AOB 10KT.
MVFR TO START OFF SUN...BEFORE LIFTING TO VFR AROUND MIDDAY AS SKIES
CLEAR OUT.
OUTLOOK 18Z SUN TO 12Z MON...VFR WITH MOSTLY CLEAR SKIES AND LIGHT
WINDS.
MARINE...
LOCAL SEA BREEZES WILL GIVE WAY TO E/NE WINDS TONIGHT...BUT AOB 10KT
ON ALL WATERS. RAIN WILL MOVE INTO REGION THIS EVENING...AND WILL
CHANGE TO SNOW LATER TONIGHT BEFORE ENDING BY DAYBREAK SUN.
NE FLOW TRIES TO STRENGTHEN ON S COASTAL WATERS SUN MORNING AS LOW
PRESSURE PASSES OFFSHORE...BUT WE EXPECT WINDS AND SEAS TO REMAIN
BELOW SMALL CRAFT ADVISORY LEVELS. WEAK HIGH PRESSURE BUILDS OVER
WATERS SUN AND SUN NIGHT.
IN THE LONG TERM...HIGH PRESSURE IN CONTROL ON MONDAY...THOUGH
SOUTHWEST WINDS WILL GUST UP TO 20 KTS LATE IN THE DAY AND MONDAY
NIGHT AS WEAK LOW PRESSURE AND FRONT APPROACH. WINDS WILL SLOWLY
SHIFT TO WEST AND NORTHWEST DURING TUESDAY AS LOW CLEARS THE COAST.
HIGH PRESSURE TAKES OVER FROM CENTRAL CANADA FOR WEDNESDAY AND
THURSDAY...WITH A NORTH TO NORTHWEST FLOW. WILL KEEP WIND GUSTS UP
TO 20 KTS. BUT NOT IMPRESSIVE COLD AIR ADVECTION NOR GOOD PRESSURE
GRADIENT AT THIS POINT SO WILL KEEP BELOW SMALL CRAFT...AT LEAST ON
THE WINDS.
WNA WAVEWATCH III MODEL TRIES TO BRING SEAS UP TO NEAR OR ABOVE 5
FEET ON THE FLOW AHEAD OF THE LOW AND FRONT MONDAY THROUGH TUESDAY
NIGHT. WENT ABOUT 1 OR 2 FEET BELOW GUIDANCE. FELT THEY WERE
OVERDONE WITH THE SOUTHWEST FLOW...BUT STILL CLOSE TO OR ABOVE SMALL
CRAFT CRITERIA FOR A TIME...UPWARDS TO 6 FEET ON THE OUTER WATERS
BOTH AHEAD AND BEHIND THE LOW AND FRONT.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...SNOW ADVISORY UNTIL 4 AM EDT SUNDAY FOR MAZ002>005-008>010-012-
026.
NH...SNOW ADVISORY UNTIL 4 AM EDT SUNDAY FOR NHZ011-015.
RI...NONE.
MARINE...NONE.
&&
$$
SHORT TERM...WTB
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
920 PM CDT SAT MAR 24 2007
.DISCUSSION UPDATE FOR TONIGHT...
920 PM
AREAL FLOOD WATCH CANCELLED AS THREAT OF ANY HEAVY FLOOD PRODUCING
RAINS NO LONGER EXISTS. FRONTAL BOUNDARY STILL RUNS FROM CENTRAL IA
ACROSS NORTHERN IL INTO NORTHERN IN AT MID EVENING.
HOWEVER...BAROCLINIC ZONE AND EFFECTIVE WARM FRONT CONTINUES LIFTING
FURTHER NORTH...WITH BAND OF OVERUNNING RAIN NOW EXTENDING FROM NE
SD ACROSS CENTRAL MN INTO W CENTRAL AND SOUTHERN WI. AIRCRAFT
TEMPERATURE AND WIND PROFILES FROM ARRIVALS AND DEPARTURES AT ORD
AND MDW SHOW THAT THE COOL LAYER ACROSS NORTHERN IL IS QUITE SHALLOW
WITH SE WINDS VEERING TO SW BY 2-3K FT ALTITUDE. SATELLITE SHOWS A
WEAK IMPULSE NNE FROM NORTHERN MO. SCT SHRA ACCOMPANED THIS FEATURE
DURING THE FIRST PART OF THE EVENING BUT RADAR COMPOSITE NOW SHOWING
A DECREASE IN ACTIVITY. WILL MAINTAIN A LOW CHC POP FOR SHRA ACROSS
MAINLY N AND NE PORTION OF FA OVERNIGHT AS THE IMPULSE MAY STILL
TRIGGER A FEW SHRA AS IT CONTINUES NEWRD. WITH MILD AND HIGER DEW
POINTS ACROSS THE HAVE BUMPED UP TEMPS A BIT OFR OVERNIGHT ALSO.
TRS
.PREVIOUS DISCUSSION...
330 PM CDT
A FLOOD WATCH WILL CONTINUE FOR THE ENTIRE AREA FOR SUNDAY AND
SUNDAY NIGHT. THERE WILL BE CHANCE OF SHOWERS AND THUNDERSTORMS
TONIGHT THROUGH MONDAY. THERE WILL BE FOG TONIGHT.
THE UPPER AIR LOW WAS OVER ARIZONA THIS MORNING AND MOVED INTO
SOUTHEAST COLORADO BY 1945 UTC. THIS IS SEEN ON THE WATER VAPOR
LOOPS. THE PROFILER WIND AT 850 SHOWS THE 30 KNOTS OR GREATER OVER
OKLAHOMA AND KANSAS. THIS IS A STRONGLY BAROCLINIC SYSTEM. THE GFS
500 MB FORECAST SHOWS HAS THE LOW OVER MINNESOTA BY 00 UTC MONDAY.
THIS PUTS A JET STREAK OVER EASTERN IOWA AND SOUTHERN WISCONSIN.
THE CHANCE OF THUNDERSTORMS AND SCATTERED THUNDERSTORMS TONIGHT AND
SUNDAY ARE FROM A SURFACE WARM FRONT MOVING NORTH. THERE WILL BE
CHANCE OF THUNDERSTORMS SUNDAY AFTERNOON AND LIKELY THUNDERSTORMS
SUNDAY NIGHT. THAT IS WHEN WE EXPECT THE STRONGEST THUNDERSTORMS...
POSSIBLY SEVERE. THE SUNDAY THUNDERSTORMS WILL BE A RESULT OF THE
UPPER LOW AND JET STREAK.
ANOTHER UPPER AIR WAVE WILL MOVE THROUGH THE MIDWEST TUESDAY. WE
WILL HAVE A CHANCE OF THUNDERSTORMS IN THE FORECAST. THE TEMPERATURE
WILL INCREASE SUNDAY THROUGH THE MIDDLE OF THE WEEK. MID TO UPPER
70S ARE FORECAST FOR HIGHS ON MONDAY.
&&
.AVIATION...
654 PM
00Z TAFS...FIRST AND MAIN CONCERN THIS PERIOD WILL BE POTENTIAL FOR
FOG AND LOW VIS. PREVAILING VIS GENERALLY 2-4SM ACROSS THE AREA WITH
SOME LOCALLY DENSE FOG ALONG THE LAKE MICHIGAN SHORE. SETUP FOR FOG
IS DIFFERENT THAN 24HRS AGO AND WHILE GUIDANCE DOES TAKE VIS/CIGS ON
THE DECK AGAIN OVERNIGHT...LOCAL FOG PREDICTOR NOT INDICATING
WIDESPREAD DENSE FOG FOR TONIGHT. NOT MUCH RAIN ACROSS THE AREA OVER
THE TAF SITES OVER THE PAST 24 HRS AND TEMPS ARE 10 DEGREES WARMER
THEN THIS TIME FRIDAY. SFC HIGH IS MOVING OFF TO THE EAST THIS
EVENING AND EXPECT SE FLOW TO SET UP...THOUGH LIGHT. WHILE LOWER
ATMOSPHERE REMAINS VERY MOIST THINK PREVAILING VIS LIKELY TO END UP
IN THE 1SM RANGE WITH USUAL LOW SPOTS DROPPING TOWARD 1/2SM.
LIKEWISE WITH SLIGHTLY BETTER VIS EXPECTED...CIGS SHOULD ALSO BE A
LITTLE HIGHER. AS WINDS TURN MORE SOUTHERLY AROUND/AFTER SUNRISE
SUNDAY...EXPECT FOG TO LIFT...LOW CLOUDS TO SCATTER OUT LEAVING A
3-5KFT STRATOCU/CU DECK FOR THE REMAINDER OF THE PERIOD.
AS FOR WINDS...ESE WINDS UNDER 10KTS GRADUALLY TURN SE OVERNIGHT
AND SPEEDS DIMINISH FURTHER TO 5KTS OR LESS. WINDS MAY BECOME LIGHT
AND VRB BUT WILL MAINTAIN SE DIRECTION FOR NOW. ONCE WINDS SWING
AROUND SOUTHERLY SUNDAY MORNING...SHOULD STEADILY INCREASE TO 10-15
KTS WITH GUSTS TO 20-22KTS...ESPECIALLY IN THE AFTERNOON. AS FOR
PRECIP...MODELS SHOW LITTLE TO FOCUS PRECIP DEVELOPMENT THRU THE
PERIOD. COULD BE A PASSING SHOWER TONIGHT...NOT WORTH MENTION AT
THIS POINT. PRECIP FOCUS SHIFTS TO THE UPPER MIDWEST SUNDAY. SOME
OF THIS ACTIVITY MAY REACH NORTHERN IL SUNDAY EVENING...WELL AFTER
THE END OF THIS PERIOD. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LM...NONE.
&&
$$
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