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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
519 PM CST Friday Nov 28 2014

Synopsis...
issued at 318 PM CST Friday Nov 28 2014

Nearly zonal flow aloft and 850 mb warm air advection is aiding to advect a warm
front into the area today. Temperatures range from the lower to middle
40s across the southern County Warning Area...and to the middle and lower 30s across the
northern County Warning Area. Satellite imagery is showing the snow pack melting
with this warm air advection. Dewpoints are rising into the upper 20s to low 30s.

&&

Short term...(this evening through saturday)
issued at 318 PM CST Friday Nov 28 2014

Main forecast concern for the short term forecast is the warm
front moving into the area tonight bringing with it a chance of
fog and possibly low level clouds.

It is clear that the models...especially the NAM do not have a
good handle on boundary layer moisture. The NAM over does the
current snow cover. With strong 850 mb warm air advection the NAM probability of precipitation low level
clouds tonight and through most of the day. The GFS has something
similar...but not as bullish. A look at the model fields and
observations leads ME to believe that there is not a good chance
for the development of low level clouds...there is not enough deep
layer moisture or forcing for cloud development. Believe that the main
threat will be fog due to overrunning warm air over a melting snow
pack. Winds are forecast to remain around 8-10kts tonight which
may inhibit fog development. This wind will make fog development
patchy tonight . High level clouds should continue to advect
through the area...also inhibiting the development of fog over a
large area.

Saturday looks to be warm with temperatures in the middle 40s to low
50s south. Did not use any of the NAM guidance for temperature forecasts
as the NAM keeps snow pack around a thus lowers temperatures. High
temperatures today were under down as 850 mb warm air advection drove temperatures higher.
The RUC had the best handle on highs and trends with temperatures today.

Long term...(saturday night through friday)
issued at 318 PM CST Friday Nov 28 2014

Saturday night...cold front to arrive northwest County Warning Area toward daybreak.
Patchy fog possible ahead of front but with American models
verifying too moist over bl and enough of gradient pre-frontal
for 5-10+ miles per hour winds and typically not favored veering
southwesterly direction I have left out any mention attim. Decent
temperature gradient by 12z sun with 20s far northwest County Warning Area Post-frontal
contrast to upper 30s and lower 40s far southeast County Warning Area.

Sunday and Sunday night...highs on Sunday to occur in the am
through midday ahead of frontal passage. Front is anticipated to
be exiting far east/southeast County Warning Area by midday. Ensuing cold
advection on brisk northwest winds 15 to 30 miles per hour will result in
falling temperatures despite decreasing clouds for at least partial PM
sunshine. Sunday night...continued clearing early with Canadian
high and attendant strong subsidence building in. Lingering pressure
gradient to maintain enough wind to prevent complete bottom out
on lows and with loss of snow cover leaned toward warmer side of
guidance blend...with mainly teens for lows with some single digits
northwest County Warning Area. These temperatures combined with winds will produce
bitter cold wind chills in single digits above and below zero
overnight into early Monday morning.

Monday and Monday night...dry and continued cold with well below
normal temperatures as Canadian high builds in. Highs Monday in the
teens and 20s. Lows Monday night in single digits to around 10
degrees. If any longer duration of light or calm winds then lows may
be still 2-4 degrees too warm some locations.

Tuesday and Tuesday night...Canadian high will shift east into the
Ohio Valley during the day on Tuesday with strengthening return
flow ushering in warmer air for rebound on temperatures into the 30s
for highs many areas. Continued southerly winds to keep lows mainly
in the 20s Tuesday night.

Wednesday through Friday...medium range models support a light precipitation
event as ejecting energy from rockies meets up with increasing
moisture. Challenge though is models continue to vary on the
timing/placement of surface and upper features and as result
instead of placing higher probability of precipitation for what is likely to be only 12
hour event at best... have placed small probability of precipitation over 24+ hour period
focusing on Thursday and Thursday night attim. Precipitation type appears
to be mainly rain but depending on timing could begin as light
wintry mix in some areas. Temperatures will continue moderating to closer
to normal during the period.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 517 PM CST Friday Nov 28 2014

As earlier afd states...the main concern for aviation could be the
development of fog or br tonight into tomorrow am. Snow melt could
lead to some visibility restrictions...especially at brl. Confidence is
low in the development of anything less than MVFR...however
guidance suggests LIFR for a large area. Believe that guidance is
doing a poor job with low level moisture so will only go MVFR at
brl and VFR elsewhere. Since nothing has changed and this is
already very well stated...in early afd issuance.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Synopsis...Gibbs
short term...Gibbs
long term...05
aviation...Ervin/Gibbs

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