2007-01-27 Wx Forecast and Discussion
Current conditions
Fog in the Valley?! You don't say!
The 500 mb cutoff low over the southwest US has moved eastward over OK. This has allowed a bit of moisture to become wrapped into the 500 mb cutoff low that now resides along the central CA coastline. Reno is reporting a SE wind direction at 500 mb, which is an indication of how broad the cutoff low has become. IPW at Bodega Bay is pushing 0.8 inches.
Like yesterday, the Valley is foggy with temperatures in the mid 30s. Temperature at Blue Canyon and Forrest Hill is in the upper 30s. At higher elevation, where there is snowpack, the temperature is well below freezing.
00-72 Hour forecast
Day 2 is the only thing to talk about in this period. As mentioned in the Current Conditions section, the cutoff low has pulled a little bit of moisture into itself. 00 UTC GFS suggests more could be on the way with values as large as 1" in the vicinity of the low. The track of the low as it opens provides some possibility of precipitation beginning as early as Saturday evening. The likelihood of precipitation exceeding 0.5" is small whether one considers the GFS and CMC ensemble or Whitaker-Hamill analogue technique. It appears the probability of >0.5" by 00 UTC Monday is 15-20%. Of course, the GSD WRF-NMM guidance crashed on the day I was at home with my strep-infected daughter. It is unavailable right now.
3-10 days
The first signs of something potentially of interest to HMT are taking form in the Western Pacific. The 00 UTC GFS shows a plume of air with IPW > 40mm moving into the mid-latitude jet stream near 140E. By 96 hours, this moisture stream has combined with a smaller one flowing out of the Tropics just south of Hawaii to form a subtropical pool of air having IPW > 40 mm extending from the dateline to 140W.
Of course much disagreement is evident amongst the CMC and GFS ensemble members beyond 96 hours. The earliest interesting situation in either ensemble occurs Feb 3-4. A couple of members have a cold event in association with the expansion and southwest movement of the Hudson bay low. A couple of members have this low flattening the ridge and producing westerly flow over N CA. While most members continue to have a high-amplitude ridge over the area, and, worse yet, some move a large trough or cutoff into old Mexico, which would divert subtropical moisture away from the ARB.
Chris Anderson GSD/FAB