AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
935 PM EST Mon Jan 9 2012


.UPDATE...
02Z Water vapor and H4 RUC analysis shows a complex upper level
pattern in place across the CONUS this evening. Main northern stream
FLOW arrives across the Pacific NW while ridging up into SC Canada.
This flow then dives back to the southeast forming longwave
troughing across the NE states and eastern Canadian Provinces. Other
feature of note, and most important to our forecast is a large
cut-off upper LOW spinning over TX. WV imagery shows abundant
MID/upper level MOISTURE streaming east/NE ahead of this feature
along the northern Gulf Coast. Synoptic support ahead of the low is
combining with deep WAA pattern to produce a large area of showers
and storms along and south of the LA coastline. This weather will
enter our forecast later Tuesday and Tuesday NIGHT, however for the
rest of the overnight, our weather will remain dry and QUIET,
outside of areas of FOG. 00Z KTLH SOUNDING shows a fairly dry
profile in the middle and lower levels this evening, however the
upper level moisture mentioned above can be seen overriding the
region above around 400mb. This moisture will be lowering with time
overnight resulting in a mostly CLOUDY forecast for your Tuesday.

Once again, fog will be the main forecast concern during the early
morning hours. HI-res guidance is generally hinting toward better
fog potential in the western zones associated with a developing weak
southerly flow. While some fog is certainly possible overnight, the
areal coverage and PERSISTENCE of the fog does not appear AS
impressive as previous nights. This is especially true noting the
amount of mid/HIGH level clouds overspreading the region which
should have some influence in slowing the radiative process. Still a
bit early in the evening to determine the degree to which this
higher level moisture will impact the fog forecast, so will not make
any significant changes with this update package.

Temperatures appear on TRACK with lows generally dropping into the
lower to middle 50s. Will expect a FEW mid/upper 40s over toward the
SE big bend and Suwannee River Valley in closer proximity to the
surface high.
...(TUESDAY THROUGH THURSDAY).
The 12 UTC model suite remains on track, bringing a strong cold
FRONT through our forecast area Wednesday morning. The NAM is still
a little slower than the global models, but the global models are a
bit slower than their previous runs so the timing differences are
smaller than 24 hours ago. With strong Q-G forcing and ample deep
layer moisture, there is almost no question as to whether or not it
will RAIN here, it`s just a matter of when. Our POP for Tuesday
night/Wednesday morning is about 80%, but this will probably come up
to near 100% in subsequent forecast packages once the timing becomes
more certain. Our STORM total QPF for this even is about an inch
areawide, but of course a few locations could get double or triple
this amount in the heavier storms. Temperatures behind this cold
front will not be very cold, and lows Thursday morning will return
to near average (lower to mid 40s) with mostly clear skies and a dry
airmass in place. A stronger (but dry) cold front will pass through
our forecast area Thursday afternoon and evening, but will not
arrive in time to prevent high temperatures from reaching the upper
60s to lower 70s.

Not much has changed with regard to the severe weather potential for
Tuesday night and Wednesday morning. All indications continue to
suggest another high-SHEAR/low CAPE environment for our region as
the SQUALL line moves through. The SPC subjective Convective
OUTLOOK the 09 UTC SREF, and our local objective severe weather
PROBABILITY forecasts show the chances for severe storms at about 5%
within 25 miles of a point. This looks reasonable based on our
experience with such cases. There may have been a subtle change in
the model forecast WIND profiles, which now suggest a less curved
HODOGRAPH (but still strong shear magnitudes). This would indicate
more of a threat for damaging wind gusts in LEWPs, and still
possibly a weak, short-lived TORNADO. This is more LIKELY where the
greatest SBCAPE coincided with the squall line, which right now
appears to be the FL Panhandle (west of the Apalachicola River). By
tomorrow the high-resolution NWP guidance will have the event within
its forecast time, and we will be able to examine UPDRAFT speeds and
HELICITY to confirm the overall severe weather threat.