SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NWS LOS ANGELES/OXNARD CA
1055 AM PDT SUN JUL 27 2008
UPDATED AVIATION SECTION
.SHORT TERM (TODAY-TUESDAY)...LATEST FOG PRODUCT IMAGERY INDICATED
LOW CLOUDS HAVE PUSHED INLAND TO THE COASTAL SLOPES OF LA/VTU AND
SBA COUNTY MTNS THIS MORNING...WHILE N OF POINT CONCEPTION STRATUS
CONTINUES TO QUICKLY APPROACH THE CENTRAL COAST AND SHOULD AFFECT
MOST COASTAL AREAS BY SUNRISE. LATEST AMDAR SOUNDING NEAR LAX SHOWS
MARINE LAYER DEPTH AT 2000 FT. WITH SFC ONSHORE GRADIENTS TRENDING
STRONGLY ONSHORE THIS MORNING...EXPECT TEMPS TO LOWER AT LEAST 5
DEGREES IN MUCH OF THE INTERIOR SECTIONS TODAY...AS WELL AS THE
INLAND COASTAL AREAS INCLUDING DOWNTOWN LOS ANGELES WHERE THE HIGH
SHOULD REACH THE LOWER 80S. WITH A STRONG ONSHORE SFC GRAD OF +10MB
BETWEEN LAX-DAG EXPECTED...GUSTY WEST TO SOUTHWEST WINDS WITH GUSTS
TO 45 MPH WILL BE LIKELY TODAY THROUGH THE EVENING HOURS...MAINLY IN
THE WESTERN PORTION AROUND LAKE PALMDALE AND POPPY PARK. A WIND
ADVISORY WILL BE ISSUED FOR THE MORNING ZONE PACKAGE. AS FAR AS THE
LA/VTU COUNTY MOUNTAINS AND ANTELOPE VALLEY TODAY...ONLY EXPECTING A
FEW CU BUILD-UPS THIS AFTERNOON AS CONVECTIVE PARAMETERS ARE NOT
IMPRESSIVE SUCH AS K-INDEX AND LIFTED INDEX. WIND PROFILES ARE NOT
CONDUCIVE FOR MONSOONAL FLOW ANY LONGER AS WEAK UPPER LOW OFF SO CAL
COAST FILLS IN AND KEEPS MONSOONAL MOISTURE WELL EAST OF FORECAST
AREA.
NOT MUCH CHANGE FOR MONDAY AND TUE AS ONLY A DEGREE OR TWO
FLUCTUATION AS ONSHORE FLOW WILL REMAIN FAIRLY STRONG MONDAY
BRINGING ANOTHER DAY OF LOCALIZED GUSTY WINDS ACROSS THE ANTELOPE
VALLEY. NOT QUITE AS STRONG AS TODAY. THICKNESS LVLS REMAIN THE SAME
AS WELL THROUGH THE PERIOD. TUE COULD BE SLIGHTLY WARMER AS ONSHORE
FLOW SHOULD BE A BIT WEAKER. EXPECT LOW CLOUDS TO CONTINUE TO AFFECT
THE COASTAL AND VALLEYS TONIGHT AND MON MORNING...BUT SHOULD BE ONLY
PATCHY ACROSS THE VALLEYS BY TUE MORNING. NOT LOOKING FOR ANY CHANCE
OF CONVECTION ACROSS THE AREA MON AND TUE AS MORE STABLE SW TO W
FLOW ALOFT WILL PERSIST THROUGH THE AREA DUE TO WEAK UPPER TROF JUST
TO THE NORTH OF THE FORECAST AREA.
.LONG TERM...(WED-SAT)
BOTH GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT THAT AN UPPER LVL
HIGH WILL NUDGE INTO SO CAL WED THROUGH SAT. THIS WILL BRING A WARM
UP THROUGH THE PERIOD. AN UPPER TROF CONTINUE TO HANG AROUND TO THE
NORTH OF THE FORECAST AREA AS WELL. THEREFORE NOT EXPECTING
SIGNIFICANT HEATING OVER THE FORECAST AREA WITH HIGHS REMAINING NEAR
NORMAL FOR THIS TIME OF YEAR. MONSOONAL MOISTURE CONTINUES TO STAY
WELL EAST OF THE AREA THROUGH THE PERIOD AS WELL.
&&
.AVIATION...27/1800Z.
AN UPPER LEVEL TROUGH OVER SOUTHERN SIERRA WILL CONTINUE MOVING
NORTHEAST WHILE AN UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC
APPROACHES NORTHERN CALIFORNIA. LIGHT UPPER LEVEL SOUTHWEST FLOW
OVER THE AREA WILL BECOME MODERATE BY THE END OF THE PERIOD. A
MODERATE ONSHORE PRESSURE GRADIENT WILL BECOME WEAK OVERNIGHT. LOW
LEVEL STRATUS TOPS WERE AROUND 020 THIS MORNING AND HEIGHT WILL
CHANGE LITTLE THROUGH THE PERIOD.
KLAX...IT IS VERY LIKELY CIGS AROUND 012 WILL DEVELOP IN THE EVENING
AND PERSIST THROUGH THE REMAINDER OF THE PERIOD.
KBUR...IT IS LIKELY CIGS AROUND 012 WILL DEVELOP LATE IN THE
EVENING.
VIRTUALLY CERTAIN - 95-100%
VERY LIKELY - 80-95%
LIKELY - 60-80%
CHANCE - 30-60%
NOT VERY LIKELY - 20% OR LESS
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXCWFLOX).
&&
$$
PUBLIC...KAPLAN
AVIATION...30
WWW.WEATHER.GOV/LOSANGELES
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NWS LOS ANGELES/OXNARD CA
1010 PM PDT FRI JUL 25 2008
.SHORT TERM (TONIGHT-MON)...ACARS SOUNDINGS FROM LAX INDICATED THE
MARINE LAYER WAS QUITE SHALLOW AT ABOUT 900 FEET OR SO. A FINGER OF
LOW CLOUDS EXTENDED TO NEAR THE VTU COAST THIS EVENING OTHERWISE LOW
CLOUDS WERE LARGELY ABSENT FROM COASTAL PORTIONS OF THE FORECAST
AREA THIS EVENING. SOME LOW CLOUDS ARE EXPECTED TO REDEVELOP AND
EXPAND ALONG THE COAST LATER TONIGHT WITH PATCHY DENSE FOG NOT OUT
OF THE QUESTION. OTHERWISE MAINLY CLEAR SKIES CAN BE EXPECTED ACROSS
THE REGION OVERNIGHT.
UPPER RIDGING WILL PERSIST OVER THE FORECAST AREA INTO SAT...THEN IT
LOOKS LIKE A VERY WEAK UPPER TROF WILL MOVE INTO THE REGION FOR SUN.
UPPER RIDGING SHOULD THEN BUILD BACK INTO THE REGION FOR MON. SOME
MID LEVEL MOISTURE IS FORECAST TO PUSH INTO THE DISTRICT FOR SAT...
AND WITH SOME WEAK INSTABILITY THERE IS A SLIGHT CHANCE OF AN
AFTERNOON AND EARLY EVENING SHOWER OR THUNDERSTORM EXPECTED IN THE
L.A./VTU MTNS AND ANTELOPE VALLEY. A FEW AFTERNOON CU BUILDUPS WILL
BE POSSIBLE FOR THIS REGION AS WELL SUN...BUT NO THUNDERSTORMS ARE
EXPECTED. OTHERWISE...THE MARINE LAYER SHOULD CONTINUE TO AFFECT
MAINLY COASTAL AREAS THRU THE PERIOD WITH VARYING AMOUNTS OF NIGHT
AND MORNING LOW CLOUDS AND FOG. TEMPS OVER THE DISTRICT THRU MON
WILL BE NEAR NORMAL ALONG THE COAST...AND GENERALLY NEAR NORMAL
INLAND...EXCEPT PERHAPS A FEW DEGREES ABOVE NORMAL FOR THE MOUNTAINS
AND ANTELOPE VALLEY.
...FROM PREVIOUS DISCUSSION...
.LONG TERM (TUE-FRI)...MEDIUM RANGE MODELS IN GOOD AGREEMENT THROUGH
TUESDAY SHOWING LITTLE CHANGE. HOWEVER, ON WED THE ECMWF, AS IT HAS
THE LAST COUPLE DAYS, IS SHOWING HIGH PRESSURE BUILDING AGAIN ACROSS
CA. MEANWHILE, THE GFS CONTINUES TO ADVERTISE A PRETTY STRONG UPPER
LOW APPROACHING WA WED, WITH A TROF LINGERING ALONG THE WEST COAST
THROUGH THE END OF THE WEEK. NEEDLESS TO SAY THE ECMWF SOLUTION
WOULD RESULT IN A SIGNIFICANT WARMING TREND, ESPECIALLY INLAND. FOR
NOW HAVE TRENDED TEMPS A COUPLE DEGREES WARMER. MONSOONAL MOISTURE
APPEARS TO STAY WELL EAST AND SOUTH OF THE AREA THROUGH THE END OF
THE WEEK, THOUGH THE ECMWF SOLUTION DOES LEAVE THE DOOR OPEN TO A
MONSOONAL SURGE SHOULD SOMETHING DEVELOP.
&&
.AVIATION...26/0505Z.
A LOW CONFIDENCE FORECAST IN LOW CLOUD COVERAGE ACROSS ALL COASTAL
SECTIONS FOR TONIGHT...WITH PERHAPS JUST KLAX HAVING THE BEST SHOT
OF IFR CIGS LATE TONIGHT. OTHERWISE VFR CONDITIONS SHOULD PREVAIL
OVER MUCH OF THE FORECAST AREA THRU SAT.
FOR KLAX...A LOW CONFIDENCE FORECAST IN IFR CIGS MOVING IN OVERNIGHT
INTO SAT MORNING. OTHERWISE GENERALLY CLEAR SKIES CAN BE EXPECTED
THRU SAT WITH SOME MVFR VSBYS AT TIMES THRU SAT MORNING POSSIBLE.
KBUR...HIGH CONFIDENCE IN CLEAR SKIES AND MVFR CONDITIONS THROUGH
SAT.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXCWFLOX).
&&
$$
PUBLIC...SIRARD/WOFFORD
AVIATION...SIRARD
WWW.WEATHER.GOV/LOSANGELES
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
205 AM CDT SAT JUL 26 2008
.DISCUSSION...
812 PM CDT
ISOLATED PERSISTENT/INTENSE THUNDERSTORM MOVING INTO SOUTHERN
WISCONSIN THAT DEVELOPED ALONG FRONT CONTINUES TO MARCH STEADILY
SOUTHEASTWARD. VISIBLE SATELLITE IMAGERY SHOWS A RATHER EXPANSIVE
REGION OF ADVECTING AND DEVELOPING EAST AND SOUTHEASTWARD AHEAD OF
THIS CONVECTION. THE STRATUS IS CERTAINLY AN INDICATION OF
STRONGER STABILITY WITH RESPECT TO BOUNDARY LAYER BASED
PARCELS. THIS WAS SOMEWHAT SAMPLED IN THE 00Z KDVN SOUNDING...THOUGH
MUCH MORE APPARENT IN A PAIR OF RECENT ACARS SOUNDINGS FROM ALO
AROUND 00Z. DIABATIC COOLING THIS EVENING WILL ONLY SERVE TO
STRENGTHEN THE SURFACE BASED STABILITY...WHICH WOULD NORMALLY
SPELL THE NEAR CERTAIN DEMISE OF THIS STORM.
THERE IS SOME UNCERTAINTY REGARDING THIS STORM`S FUTURE GIVEN THE
PRESENCE OF FAIRLY IMPRESSIVE ELEVATED INSTABILITY...WITH A
SECONDARY THETA-E MAX IN THE KDVN SOUNDING AROUND 850MB. PARCELS
LIFTED FROM THIS LEVEL...WHICH IS ABOVE THE MORE STABLE LAYER THAT
THE STRATUS IS DEVELOPING IN...WILL HAVE 500+ J/KG OF CAPE. GIVEN
THE ELEVATED INSTABILITY ITS NOT ENTIRELY OUT OF THE QUESTION THAT
THIS STORM COULD LINGER FOR ANOTHER COUPLE HOURS AS IT HEADS FOR
THE IL BORDER...THOUGH IF IT DOES SURVIVE ACROSS THE BORDER I
THINK N. IL WILL BECOME IT`S DEATH BED AS WEAKER LAPSE RATES AND A
PRONOUNCED WARM LAYER EVIDENT ON RECENT ACARS SOUNDINGS FROM
ORD/BMI SHOULD RESULT IN ITS DEATH.
REALLY OTHER THAN THIS ONE STORM...IT APPEARS AS THOUGH THE
CONVECTIVE POTENTIAL IN OUR CWA IS FAIRLY LOW TONIGHT. WILL BE
MAKING SOME TWEAKS TO FIRST PERIOD GRIDS TO GENTLY EASE OUR FOOT
OFF THE POPS ACCELERATOR...THOUGH WITH FRONT APPROACHING PROBABLY
WOULDN`T BE WISE TO COMPLETELY YANK PRECIP FROM FORECAST.
IZZI
.PREV DISCUSSION...
307 PM CDT
MAIN FOCUS OVER THE FORECAST PERIOD ARE ON THE CHANCES OF
THUNDERSTORMS OFF AND ON THROUGHOUT THE NEXT WEEK.
BEST CHANCES FOR ANY ACTIVITY TONIGHT WILL BE RIGHT ALONG OR OUT
AHEAD OF THE COLD FRONT IN CENTRAL IOWA AND SHORTWAVE TROF IN
CENTRAL MINNESOTA. SPC MESOANALYSIS PAGE SHOWS THAT SFC BASED CIN
HAS ERODED...BUT ACARS SOUNDINGS OUT OF ORD STILL SHOW A DECENT
CAP AROUND 700MB. WHILE SOME SCATTERED CONVECTION APPEARS POSSIBLE
WITH FURTHER DESTABILIZATION THIS AFTERNOON...IT WILL LIKELY BE VERY
SCATTERED AND NOT TOO INTENSE. SPC SHIFTED THE DAY 1 SLIGHT RISK
FURTHER EAST WITH THEIR AFTERNOON UPDATE...BUT OVERALL DYNAMICS DO
NOT SEEM ALL THAT IMPRESSIVE FOR OUR REGION. 0-6KM SHEAR WILL BE
ON THE INCREASE AS THE SHORTWAVE DROPS SOUTHWARD TONIGHT...BUT
TIMING OF THE FRONT FIRST GETTING INTO NORTHERN ILLINOIS AROUND
06Z AND THE LACKING OF ANY SORT OF LOW LEVEL JET DOES NOT BODE
WELL FOR ANY ONGOING CONVECTION. WITH AMPLE MOISTURE RETURNING TO
THE REGION EARLIER THIS AFTERNOON WITH SFC DEW POINTS INTO THE
MID/UPPER 60S...A DECENT LIFTING MECHANISM...AND FORECAST
SOUNDINGS SHOWING UPWARD OF 1000 J/KG OF ELEVATED
INSTABILITY...STILL SHOULD SEE SOME SHOWERS AND STORMS OVERNIGHT
BUT LIKELY NOT SEVERE.
HIGH PRESSURE WILL THEN SETTLE IN ACROSS THE REGION ON SATURDAY
BRINGING THE MORE COMFORTABLE AIR MASS WITH DEW POINTS DOWN AROUND
60 INTO THE REGION. SATURDAY WILL LIKELY BE THE WINNER OF THE TWO
WEEKEND DAYS AS THERE APPEARS THE POSSIBILITY OF AN MCS PLOWING
THROUGH NORTHERN/CENTRAL ILLINOIS ON SUNDAY. IT APPEARS THAT
A CLUSTER OF STORMS WILL EITHER BE ON-GOING OR DEVELOPING IN
WESTERN IOWA EARLY SUNDAY MORNING AND PROPAGATING EASTWARD ALONG
THE NOSE OF A FAIRLY FOCUSED 30-40KT LOW LEVEL JET. THIS LLJ IS
EXPECTED TO TILT SOUTHEAST AND END UP AIMING AT CENTRAL ILLINOIS
BY MID-AFTERNOON SUNDAY ACCORDING TO THE NAM. THE GFS IS
DOWNPLAYING THIS SCENARIO A BIT AND REALLY JUST HAS SCATTERED
CONVECTION OUT THERE...WHICH MAKES IT LOOK LIKE AN OUTLIER AT THIS
POINT. WITH THIS LLJ NOSE DIGGING SOUTH OF US AND CORFIDI VECTORS
AIMING THAT WAY AS WELL...THINK THAT THE BEST SHOT FOR GETTING THE
WORST PART OF THE MCS WILL LIKELY BE FURTHER SOUTH WITH THE
OVERHANG MORE LIKELY TO BE ACROSS NORTHERN ILLINOIS. THIS WILL
LIKELY CAUSE TEMPERATURES TO BE A LITTLE LOWER THAN WHAT GUIDANCE
IS PUTTING OUT THERE.
NOT MANY CHANGES TO THE UPPER LEVEL PATTERN EXPECTED OVER THE
EXTENDED PERIOD AS A LONG WAVE TROF SITS ACROSS THE EASTERN US
WITH AN AMPLIFYING RIDGE ACROSS THE ROCKIES. WITH THIS SORT OF SET
UP...WILL HAVE TO WATCH FOR ANY SHORTWAVES DIGGING DOWN THROUGH
THE FLOW AND JUST HIT THOSE PERIOD UP FOR THE BEST CHANCES OF
PRECIP. THE GFS MAY BE A BIT ANOMALOUS WITH THEIR 12Z RUN WITH THE
FAIRLY DEEP SFC LOW COMING THROUGH WISCONSIN ON TUESDAY...SO
PRETTY MUCH STAYED THE COURSE ON PRECIP CHANCES ON TUESDAY NIGHT
INTO VERY EARLY THURSDAY MORNING. TEMPERATURES WILL LIKELY NOT
FLUCTUATE MUCH OVER THIS PERIOD AND REMAIN RATHER SEASONABLE.
HALBACH
&&
.AVIATION...
06Z TAFS...MAIN CONCERNS THIS PERIOD ARE 2-4KFT CIGS CURRENTLY
ACROSS NORTHERN IL ALONG WITH FOG POTENTIAL THRU MID MORNING.
SOUTHERN EDGE OF CLOUDS GENERALLY 2-3KFT THEN LIFTS TO 3-4KFT ON
THE NORTHERN EDGE TOWARD THE IL/WI BORDER. CURRENT MOTION HAS BACK
EDGE CLEARING ORD/MDW BY 09Z. HOWEVER...MORE DEVELOPMENT RECENTLY
NOTED NEAR RFD. HAVE OPTED TO TEMPO A MVFR CIG FOR A FEW HRS BUT
OVERALL EXPECT PREVAILING CIGS OF 3-4KFT OR HIGHER. TREND WILL BE
FOR SKIES TO SCATTER AND CLEAR BY/AFTER SUNRISE. A WEAK COLD FRONT
CONTINUES TO PUSH SOUTHEAST ACROSS WI. LOW LEVELS REMAIN QUITE
MOIST AHEAD OF THIS FRONT SO ONCE LOW CLOUDS SCATTER OUT/SHIFT
EAST...EXPECT SOME 3-6SM AND LIGHT FOG UNTIL DRIER AIR ARRIVES.
FEW/SCT CU POSSIBLE LATER THIS MORNING INTO THIS AFTERNOON. LIGHT
WESTERLY WINDS WILL BECOME WNW OVERNIGHT THEN TURN NW DURING THE
MORNING. SPEEDS LIKELY TO INCREASE TO 10-15KTS THEN DIMINISH
QUICKLY WITH SUNSET. CMS
&&
.MARINE...
205 AM...LOW PRESSURE NEAR JAMES BAY WILL SLOWLY LIFT NORTHEAST
ACROSS NORTHERN QUEBEC TONIGHT AND SUNDAY. WEAK HIGH PRESSURE
EXTENDS ACROSS THE NORTHERN AND CENTRAL PLAINS. THIS HIGH WILL
SLIDE SOUTHEAST ACROSS THE OHIO VALLEY TONIGHT...A LITTLE FURTHER
SOUTH THAN THE MODELS HAD IT 24 HRS AGO. AS A RESULT...EXPECT MORE
OF A NORTHWEST WIND ACROSS THE LAKE...THOUGH STILL BECOMING LIGHT
ACROSS THE SOUTHERN END OF LAKE MICHIGAN AS THE HIGH APPROACHES
THIS AFTERNOON. THE GRADIENT ACROSS THE NORTHERN END OF LAKE
MICHIGAN REALLY DOESN/T CHANGE MUCH UNTIL SUNDAY...SO EXPECT A
PREVAILING WESTERLY WIND 10-15KTS WITH A FEW HIGHER GUSTS AT
TIMES. ANOTHER WEAK HIGH SETTLES ACROSS THE WESTERN LAKES SUNDAY
NIGHT INTO MONDAY MORNING. WINDS WILL TURN NORTH THEN BECOME LIGHT
AND VRB MONDAY MORNING BEFORE TURNING EASTERLY AS THIS HIGH
SHIFTS EAST MONDAY INTO MONDAY NIGHT. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1237 AM CDT SAT JUL 26 2008
.DISCUSSION...
812 PM CDT
ISOLATED PERSISTENT/INTENSE THUNDERSTORM MOVING INTO SOUTHERN
WISCONSIN THAT DEVELOPED ALONG FRONT CONTINUES TO MARCH STEADILY
SOUTHEASTWARD. VISIBLE SATELLITE IMAGERY SHOWS A RATHER EXPANSIVE
REGION OF ADVECTING AND DEVELOPING EAST AND SOUTHEASTWARD AHEAD OF
THIS CONVECTION. THE STRATUS IS CERTAINLY AN INDICATION OF
STRONGER STABILITY WITH RESPECT TO BOUNDARY LAYER BASED
PARCELS. THIS WAS SOMEWHAT SAMPLED IN THE 00Z KDVN SOUNDING...THOUGH
MUCH MORE APPARENT IN A PAIR OF RECENT ACARS SOUNDINGS FROM ALO
AROUND 00Z. DIABATIC COOLING THIS EVENING WILL ONLY SERVE TO
STRENGTHEN THE SURFACE BASED STABILITY...WHICH WOULD NORMALLY
SPELL THE NEAR CERTAIN DEMISE OF THIS STORM.
THERE IS SOME UNCERTAINTY REGARDING THIS STORM`S FUTURE GIVEN THE
PRESENCE OF FAIRLY IMPRESSIVE ELEVATED INSTABILITY...WITH A
SECONDARY THETA-E MAX IN THE KDVN SOUNDING AROUND 850MB. PARCELS
LIFTED FROM THIS LEVEL...WHICH IS ABOVE THE MORE STABLE LAYER THAT
THE STRATUS IS DEVELOPING IN...WILL HAVE 500+ J/KG OF CAPE. GIVEN
THE ELEVATED INSTABILITY ITS NOT ENTIRELY OUT OF THE QUESTION THAT
THIS STORM COULD LINGER FOR ANOTHER COUPLE HOURS AS IT HEADS FOR
THE IL BORDER...THOUGH IF IT DOES SURVIVE ACROSS THE BORDER I
THINK N. IL WILL BECOME IT`S DEATH BED AS WEAKER LAPSE RATES AND A
PRONOUNCED WARM LAYER EVIDENT ON RECENT ACARS SOUNDINGS FROM
ORD/BMI SHOULD RESULT IN ITS DEATH.
REALLY OTHER THAN THIS ONE STORM...IT APPEARS AS THOUGH THE
CONVECTIVE POTENTIAL IN OUR CWA IS FAIRLY LOW TONIGHT. WILL BE
MAKING SOME TWEAKS TO FIRST PERIOD GRIDS TO GENTLY EASE OUR FOOT
OFF THE POPS ACCELERATOR...THOUGH WITH FRONT APPROACHING PROBABLY
WOULDN`T BE WISE TO COMPLETELY YANK PRECIP FROM FORECAST.
IZZI
.PREV DISCUSSION...
307 PM CDT
MAIN FOCUS OVER THE FORECAST PERIOD ARE ON THE CHANCES OF
THUNDERSTORMS OFF AND ON THROUGHOUT THE NEXT WEEK.
BEST CHANCES FOR ANY ACTIVITY TONIGHT WILL BE RIGHT ALONG OR OUT
AHEAD OF THE COLD FRONT IN CENTRAL IOWA AND SHORTWAVE TROF IN
CENTRAL MINNESOTA. SPC MESOANALYSIS PAGE SHOWS THAT SFC BASED CIN
HAS ERODED...BUT ACARS SOUNDINGS OUT OF ORD STILL SHOW A DECENT
CAP AROUND 700MB. WHILE SOME SCATTERED CONVECTION APPEARS POSSIBLE
WITH FURTHER DESTABILIZATION THIS AFTERNOON...IT WILL LIKELY BE VERY
SCATTERED AND NOT TOO INTENSE. SPC SHIFTED THE DAY 1 SLIGHT RISK
FURTHER EAST WITH THEIR AFTERNOON UPDATE...BUT OVERALL DYNAMICS DO
NOT SEEM ALL THAT IMPRESSIVE FOR OUR REGION. 0-6KM SHEAR WILL BE
ON THE INCREASE AS THE SHORTWAVE DROPS SOUTHWARD TONIGHT...BUT
TIMING OF THE FRONT FIRST GETTING INTO NORTHERN ILLINOIS AROUND
06Z AND THE LACKING OF ANY SORT OF LOW LEVEL JET DOES NOT BODE
WELL FOR ANY ONGOING CONVECTION. WITH AMPLE MOISTURE RETURNING TO
THE REGION EARLIER THIS AFTERNOON WITH SFC DEW POINTS INTO THE
MID/UPPER 60S...A DECENT LIFTING MECHANISM...AND FORECAST
SOUNDINGS SHOWING UPWARD OF 1000 J/KG OF ELEVATED
INSTABILITY...STILL SHOULD SEE SOME SHOWERS AND STORMS OVERNIGHT
BUT LIKELY NOT SEVERE.
HIGH PRESSURE WILL THEN SETTLE IN ACROSS THE REGION ON SATURDAY
BRINGING THE MORE COMFORTABLE AIR MASS WITH DEW POINTS DOWN AROUND
60 INTO THE REGION. SATURDAY WILL LIKELY BE THE WINNER OF THE TWO
WEEKEND DAYS AS THERE APPEARS THE POSSIBILITY OF AN MCS PLOWING
THROUGH NORTHERN/CENTRAL ILLINOIS ON SUNDAY. IT APPEARS THAT
A CLUSTER OF STORMS WILL EITHER BE ON-GOING OR DEVELOPING IN
WESTERN IOWA EARLY SUNDAY MORNING AND PROPAGATING EASTWARD ALONG
THE NOSE OF A FAIRLY FOCUSED 30-40KT LOW LEVEL JET. THIS LLJ IS
EXPECTED TO TILT SOUTHEAST AND END UP AIMING AT CENTRAL ILLINOIS
BY MID-AFTERNOON SUNDAY ACCORDING TO THE NAM. THE GFS IS
DOWNPLAYING THIS SCENARIO A BIT AND REALLY JUST HAS SCATTERED
CONVECTION OUT THERE...WHICH MAKES IT LOOK LIKE AN OUTLIER AT THIS
POINT. WITH THIS LLJ NOSE DIGGING SOUTH OF US AND CORFIDI VECTORS
AIMING THAT WAY AS WELL...THINK THAT THE BEST SHOT FOR GETTING THE
WORST PART OF THE MCS WILL LIKELY BE FURTHER SOUTH WITH THE
OVERHANG MORE LIKELY TO BE ACROSS NORTHERN ILLINOIS. THIS WILL
LIKELY CAUSE TEMPERATURES TO BE A LITTLE LOWER THAN WHAT GUIDANCE
IS PUTTING OUT THERE.
NOT MANY CHANGES TO THE UPPER LEVEL PATTERN EXPECTED OVER THE
EXTENDED PERIOD AS A LONG WAVE TROF SITS ACROSS THE EASTERN US
WITH AN AMPLIFYING RIDGE ACROSS THE ROCKIES. WITH THIS SORT OF SET
UP...WILL HAVE TO WATCH FOR ANY SHORTWAVES DIGGING DOWN THROUGH
THE FLOW AND JUST HIT THOSE PERIOD UP FOR THE BEST CHANCES OF
PRECIP. THE GFS MAY BE A BIT ANOMALOUS WITH THEIR 12Z RUN WITH THE
FAIRLY DEEP SFC LOW COMING THROUGH WISCONSIN ON TUESDAY...SO
PRETTY MUCH STAYED THE COURSE ON PRECIP CHANCES ON TUESDAY NIGHT
INTO VERY EARLY THURSDAY MORNING. TEMPERATURES WILL LIKELY NOT
FLUCTUATE MUCH OVER THIS PERIOD AND REMAIN RATHER SEASONABLE.
HALBACH
&&
.AVIATION...
06Z TAFS...MAIN CONCERNS THIS PERIOD ARE 2-4KFT CIGS CURRENTLY
ACROSS NORTHERN IL ALONG WITH FOG POTENTIAL THRU MID MORNING.
SOUTHERN EDGE OF CLOUDS GENERALLY 2-3KFT THEN LIFTS TO 3-4KFT ON
THE NORTHERN EDGE TOWARD THE IL/WI BORDER. CURRENT MOTION HAS BACK
EDGE CLEARING ORD/MDW BY 09Z. HOWEVER...MORE DEVELOPMENT RECENTLY
NOTED NEAR RFD. HAVE OPTED TO TEMPO A MVFR CIG FOR A FEW HRS BUT
OVERALL EXPECT PREVAILING CIGS OF 3-4KFT OR HIGHER. TREND WILL BE
FOR SKIES TO SCATTER AND CLEAR BY/AFTER SUNRISE. A WEAK COLD FRONT
CONTINUES TO PUSH SOUTHEAST ACROSS WI. LOW LEVELS REMAIN QUITE
MOIST AHEAD OF THIS FRONT SO ONCE LOW CLOUDS SCATTER OUT/SHIFT
EAST...EXPECT SOME 3-6SM AND LIGHT FOG UNTIL DRIER AIR ARRIVES.
FEW/SCT CU POSSIBLE LATER THIS MORNING INTO THIS AFTERNOON. LIGHT
WESTERLY WINDS WILL BECOME WNW OVERNIGHT THEN TURN NW DURING THE
MORNING. SPEEDS LIKELY TO INCREASE TO 10-15KTS THEN DIMINISH
QUICKLY WITH SUNSET. CMS
&&
.MARINE...
124 PM CDT
THE LOW OVER MANITOBA WILL MOVE EAST AND DECREASE IN PRESSURE BY THE
TIME IT REACHES JAMES BAY...SATURDAY NOON. THE INCREASE PRESSURE
GRADIENT OVER SOUTHERN ONTARIO WILL GIVE A WIND OF 15 TO 25 KNOTS
OVER THE NORTHERN HALF OF LAKE MICHIGAN TONIGHT AND SATURDAY. AS THE
LOW MOVES EAST A COLD FRONT WILL MOVE ACROSS LAKE MICHIGAN TONIGHT
AND EARLY SATURDAY. THERE WILL BE A CHANCE OF THUNDERSTORMS ACROSS
THE LAKE TONIGHT. WILL FORECAST SLOWER WIND SPEED FOR THE SOUTHERN
HALF OF LAKE MICHIGAN TONIGHT AND SATURDAY. THE WIND IS EXPECTED TO
SHIFT TO THE NORTHWEST ACROSS ALL OF LAKE MICHIGAN BY 12 UTC
SATURDAY. BY SUNDAY THE WIND IS EXPECTED TO DECREASE OVER THE SOUTH
HALF OF THE LAKE. A HIGH WILL MOVE INTO CENTRAL ILLINOIS. THE STRONG
LOW OVER HUDSON BAY WILL PROVIDE ENOUGH PRESSURE GRADIENT OVER
SOUTHERN ONTARIO FOR THE WIND TO BE 10 TO 20 KNOTS OVER THE NORTH
HALF OF LAKE MICHIGAN.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
839 PM CDT SUN JUL 27 2008
.DISCUSSION...
CONVECTION REALLY NEVER COULD GET GOING LATE AFTN AND EARLY EVNG.
BASED ON MID TO LATE AFTN TAMDAR SOUNDINGS...AND LOOKING AT 00Z
RAOBS FROM ABR/OAX...ANYTHING REMOTELY SFC BASED ALG OUTFLOW/WMFNT
BNDRY NR MO RVR PRACTICALLY IMPOSSIBLE TO INITIATE WITH 150-200J/KG
CAP. THIS IS NOT TO DISCOUNT THE TREMENDOUS LARGER SCALE SUBSIDENCE
PRESENT WITHIN INTENSE DRYING ON WV ACRS ALMOST ENTIRE REGION BEHIND
THE DEPARTING MCV ENHANCED CONVECTION IN IA/MO AND THE UPR WAVE ACRS
SERN MN. OVERALL...CONVECTIVE POTENTIAL OVERNIGHT LOOKS FAIRLY
DISMAL. HAVE THE EDGE OF THE WK MID LVL ISENTROPIC LIFT LINGERING
THRU THE FAR ERN CWA THIS EVNG...WITH BEST OF MEAGER CHC FOR
REDEVELOPMENT THRU NW IA LATER EVNG. PERHAPS GETTING AN EDGE OF CAP
BOOST AS WELL LATER TONIGHT OVR THE FAR NERN CWA...BUT STILL SITTING
AT A SUBCLIMATOLOGICAL 20 POP WITH LACK OF STRONG LLJ.
OTHERWISE...WK LOW LVL CONVERGENCE NOW CENTERED IN FAR SWRN CWA WITH
SFC BNDRY NOW BACKED SWRD INTO NERN NEBRASKA. SFC MOISTURE REMAINS
HIGH WITH DWPTS IN THE UPPER 60S TO MID 70S. WL ADD IN SOME PATCHY FOG
IN AREA JUST ON THE COOL SIDE OF THE BOUNDARY WHERE LOW LVL
STABILITY WL BE A BIT HIER...AS WELL AS WHERE RECENT RAINFALL HAS
BEEN SLIGHTLY GREATER. REMAINDER OF THE FCST FAIRLY WITHIN THE
TWEEKING REALM...WITH SOME INCREASE IN LOWS ACRS SRN CWA DUE TO
MOISTURE CONTENT OF AIRMASS.
&&
.AVIATION...
MOISTURE TRAPPED IN A STABLE LAYER BENEATH SUBSTANCE INVERSION ALOFT
WILL BE PRIMARY AVIATION CONCERN OVERNIGHT. MVFR CIGS WILL LIKELY
EXPAND ACROSS THE CWA AND GRADUALLY LOWER AS THE NIGHT WEARS
ON...LIKLEY APPROACHING IFR CIGS TOWARD MONDAY MORNING AT ALL THREE
TAF SITES. WITH THE RECENT RAIN...AND LIGHT SFC WINDS OVERNIGHT SOME
IFR VSBYS IN FOG ALSO A REAL POSSIBILITY...ESPECIALLY ARND KSUX
WHERE EVENING DEW PTS ARE STILL IN THE MID 70S. SOME WIDELY
SCATTERED CONVECTION COULD GO LATE TONIGHT ACROSS THE NORTHERN PART
OF THE CWA BUT NOT ENOUGH THREAT TO MENTION IN THE KHON TAF AT THIS
TIME. LATE JULY SUN SHOULD LIFT AND THEN BURN OFF MVFR CIGS/FOG BY
14-15Z MONDAY MRNG.
&&
.PREV DISCUSSION...
WEAKER CONVECTION TO CONTINUE ALONG AND NORTH OF I-90 THROUGH LATE
AFTERNOON...BUT AREA OF BEST CONVECTION WILL BE ALONG MISSOURI
RIVER INTO NORTHWEST IOWA...SOUTH OF WHERE LINE OF CONVECTION IS
FIRING ALONG THE OUTFLOW BOUNDARY AT 19Z. THIS BOUNDARY...ALONG WITH
THE SURFACE WARM FRONT IN NORTHERN NEBRASKA AND CENTRAL IOWA WILL
ACT AS FOCUS. MODEL CAPES IN EXCESS OF 3000 J/KG WITH 100-200 M2/S2
HELICITY VALUES CENTERED OVER NORTHEASTERN NEBRASKA AND WESTERN IOWA
FROM MID AFTERNOON THROUGH THIS EVENING. CUMULUS STARTING TO POP
ALONG MISSOURI RIVER AT 19Z AS TEMPERATURES REACH THE MID 80S WITH
LOWER 70S DEWPOINTS. SHOULD SEE STORMS GO SEVERE IN THESE AREAS
RATHER QUICKLY ONCE THEY GET GOING LATER THIS AFTERNOON. LARGE HAIL
AND WIND WILL BE THE MAIN THREAT. BY MID EVENING... FRONTAL BOUNDARY
GETS PUSHED SOUTH INTO EASTERN NEBRASKA AND SOUTHEAST IOWA...SO
NEARLY ALL OF THE ACTIVITY WILL BE OUT OF THE CWA BY 03Z. WILL STILL
HAVE A SLIGHT CHANCE OF ELEVATED SHOWERS AND THUNDERSTORMS IN THE
EXTREME NORTHERN PORTIONS OF THE AREA AFTER MIDNIGHT ALONG A WEAK
MID LEVEL BOUNDARY.
MESSY WEATHER PATTERN CONTINUES INTO MONDAY AS ANOTHER WAVE AND
LINGERING LOW LEVEL BOUNDARY SHOULD PROVIDE THE FOCUS FOR
THUNDERSTORM DEVELOPMENT LATE IN THE AFTERNOON AND EARLY IN THE
EVENING OVER CENTRAL SD. PLENTY OF INSTABILITY ALONG WITH GOOD SHEAR
SHOULD LEADS TOWARDS A GOOD CHANCE FOR SEVERE WEATHER IN THE EVENING
WEST OF INTERSTATE 29 AND EAST AFTER ABOUT MIDNIGHT...ALTHOUGH THE
THREAT SHOULD WANE SOME. DELTA THETA E DIFFERENCE APPROACHING 40 SO
IF WE CAN GET AN MCS GOING THE THREAT FOR SEVERE WINDS LOOKS PRETTY
STRONG.
OUTSIDE OF A CHANCE FOR THUNDERSTORMS ON MAINLY TUESDAY MORNING OVER
THE EASTERN CWA...SHOULD SEE A GOOD CHANCE FOR DRY WEATHER TUESDAY
AFTERNOON AND EVENING.
THE CHANCE FOR THUNDERSTORMS WILL RETURN ON WEDNESDAY NIGHT BUT
PLACEMENT FOR BEST CHANCE NOT EASY AND WILL CARRY MAINLY A 20 TO 40
PP FOR NOW.
IN THE LATTER PERIODS(THU-SUN)...NOT MANY CHANGES PLANNED AS
CLIMATOLOGY NOT A BAD FIRST GUESS. LOWS SHOULD MAINLY BE IN THE 60S
WITH HIGHS MAINLY FROM THE MID 80S TO MID 90S. LOOKS LIKE RELATIVELY
STRONG NORTHWEST FLOW ALOFT WILL DEVELOP BY THE WEEKEND WITH A
STRONG RIDGE BUILDING OVER THE WESTERN HIGH PLAINS. THE FASTER
WESTERLY FLOW THAT HAS BROUGHT ABOUT THE BUSY WEATHER THIS PAST WEEK
LOOKS TO SHIFT FARTHER NORTHWEST AND REMAIN THERE UNTIL AT LEAST
EARLY NEXT WEEK. NEWEST GFS A LITTLE QUICKER TO KNOCK DOWN THIS
RIDGE THAN YESTERDAY AND WILL STILL LOOK FOR THE CHANCE OF SOME REAL
SUMMERTIME HEAT BUILDING IN FOR THE WEEKEND AND EARLY NEXT WEEK.
CHANCES FOR THUNDERSTORMS PRETTY LOW AND WILL GENERALLY KEEP POPS OF
10 OR LESS THROUGH THE PERIOD. GILLISPIE/08
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
CHAPMAN/HARMON
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