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fxus63 klsx 150510 

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
1110 PM CST Thu Nov 14 2019

Short term... (through late Friday night)
issued at 312 PM CST Thu Nov 14 2019

Conditions are expected to be favorable for radiational cooling
tonight due to the presence of a ridge axis overhead in the wake
of a cold front. The ridge axis will ensure light winds and
limited cloud cover for most of the region tonight. Satellite
imagery of the lingering Snow Field across the region indicates
that substantial melting occurred today, which means that a fair
amount of moisture has been added to the lowest level of the
atmosphere. The combination of favorable radiational cooling
conditions in the presence of added moisture suggests that
radiation fog could develop tonight after 03z and especially after
06z. This is consistent with BUFKIT profiles. However, given the
cold air temperatures expected tonight, it is not immediately
clear whether the prevailing physical mechanism would be
condensation (from water vapor into liquid fog droplets) or
deposition (from water vapor into solid frost). Either way, this
could produce patchy slick spots given the cold surfaces expected

A gradual warming trend will continue on Fri with both highs and
lows expected to be a few degrees warmer than they were on Thu. No
precipitation is expected during this time.


Long term... (saturday through next thursday)
issued at 312 PM CST Thu Nov 14 2019

The gradual warming trend is expected to continue through the
middle/end of next week. By the end of the week, highs should be
in the upper 40s to lower 50s and lows should be in the 30s.

Overall, there appear to be few opportunities for precipitation
during the extended forecast period. One of these opportunities is
associated with a pv anomaly and its induced trough as they
approach and then move through the region on Sat night into
Sunday. At this time, precipitation chances appear limited to the
northern part of the lsx County Warning Area on Sunday. Precipitation types will
depend on timing details which are poorly resolved this far in
advance, but any mixed precipitation should change over to rain
as temperatures warm during the day.

The next opportunity for widespread precipitation appears to be
during Wed-Fri when a deep trough develops over the western Continental U.S.
And a cutoff upper low over socal drifts eastward. The resulting
southwesterly flow aloft and isentropic ascent could produce light
precipitation during this time. There is a fair amount of
uncertainty due to model differences regarding the timing,
strength, and placement of important features such as the upper
low center.



Aviation... (for the 06z tafs through 06z Friday night)
issued at 1110 PM CST Thu Nov 14 2019

VFR conditions, light surface winds, and dry weather are expected
to prevail at the taf sites through much of the valid period. The
main exception will be fog early Friday morning, where despite
opposition of nearly all guidance, conceptual models support some
fog potential due to recent snowmelt across the region and ideal
radiational cooling conditions.



Lsx watches/warnings/advisories...

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