Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252022

Area Forecast Discussion
National Weather Service Des Moines IA
222 PM CST Tue Feb 25 2020

.DISCUSSION.../Tonight through Tuesday/
Issued at 221 PM CST Tue Feb 25 2020

Main Points

Fairly quiet weather expected through the next several days. Light
snow possible in portions of far southern Iowa this evening into
tonight as a low pressure system skirts the area. Additional light
snowfall may be seen in north central Iowa. Not expecting much at
all for accumulations or travel impacts out of this wintry
precipitation. Near to below normal temperatures hang around through
the end of the week, but a warm up is in store for the weekend which
should send our highs back into the 40s and 50s. Next chances for
widespread precipitation may move back into the area early next week.


At 20z GOES water vapor imagery depicts a strong pv anomaly
digging south through the central High Plains, part of broader
synoptic scale troughing encompassing the central tier of the
conus. Another weaker wave was evident over central Illinois but
steadily deamplifying as it ejects northeast through the mean flow
aloft. A stout layer of mid-level dry air has effectively shut
off any precipitation associated with the latter lead wave as it
clipped far southern Iowa. Surface observations beneath radar
echoes have remained dry through the day. The more significant
trailing wave pushes eastward this evening into tonight. Some
light snow will be possible again as upper level forcing again
clips far south central and southeastern Iowa, but expect dry air
to remain a mitigating factor and keep any accumulations to a
dusting or a few tenths of an inch. Hi-res models continue to
suggest another possible area for light snow tonight over north
central Iowa. Persistent cold air advection keeps near-surface
lapse rates steep after dark and could trigger a few areas of
light snow or a wintry mix. Confidence in coverage and p-type is
quite low due to dry air and degree of ice introduction into the
saturated layer, but regardless precip amounts will be light with
minimal to no impact.

Trough pushes east on Wednesday and northwesterly flow aloft becomes
established for the next several days. This will keep
temperatures near to below normal for late February. Rather weak
surface pressure gradient over the state should keep winds
relatively light Thursday through the end of the week. A few weak
waves cross through the mean flow but dry air limits most precip
potential. Only time frame with low chance PoPs through this
period is Friday night, but confidence in that amounting to
anything notable is quite low. Temperatures rebound this weekend
as a ridge builds over the central conus. NBM has consistently
been too cool on our warmer days of late, so opted to give
forecast highs a nudge above guidance for Saturday. Forecast for
Sunday could still be too cool as well, but more cloud cover may
be around to limit warming and hinders confidence at this time.
Chances for precip return next week as a trough digs out west.
Southerly surface flow should bring Gulf moisture northward toward
the area and interact with a surface warm front draped somewhere
across the central Plains. Models will likely waver with their QPF
axis over the next several days until key synoptic features
become more clear.


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1121 AM CST Tue Feb 25 2020

VFR conditions prevail through the afternoon hours. MVFR cigs
expected to develop after 00z across most of the area. Model
guidance suggests temporary improvements back into VFR overnight,
but forecast confidence is rather low in timing/location of these
areas at this time.




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