Scientific Forecaster Discussion
fxus63 koax 252046
Area forecast discussion
National Weather Service Omaha/valley NE
346 PM CDT Mon Sep 25 2017
Short term...(tonight through thursday)
issued at 330 PM CDT Mon Sep 25 2017
..a wet start to the week, but cooler/drier the next several days...
Forecast concerns in the short term will primarily be the ending of
the showers and thunderstorms, then cooler temperatures for the rest
of the week.
Rainfall amounts varied from zero for parts of southeast Nebraska
and parts of southwest Iowa to 2.76" at the National Weather Service Omaha/valley
office through 7am. A 2" plus band extended through parts of
counties. Toward Nebraska City and southeast of there...very
little rain prior to 7am.
The latest subjective surface analysis highlighted a cold front over
southeast Nebraska and southwest Iowa at noon. Surface
temperatures were in the 80s at noon at Falls City and Clarinda
with calm winds. Meanwhile, to the north, the winds were from the
north and mostly in the 50s and 60s with abundant
cloudcover/precipitation. By 3pm...the surface front had pushed
southeast...but had not made it to St. Joseph yet.
Showers covered much of the forecast area and were generally Post-
frontal at noon...however the focus by 3pm had shifted closer the
the front from northeast Kansas and southeast Nebraska into
southwest to central Iowa. 20z Storm Prediction Center mesoanalysis shows surface
based cape of 1000-2000j/kg near the front over southeast
Nebraska and southwest Iowa southeastward with steep mid-layer
lapse rates/precipitable water of 1.5-1.7 inches just behind the surface front
(ahead of the h85 front) in a zone of h85 warm air advection/mid
Water vapor satellite imagery/the h50 pattern depict a closed low
pressure system over southeast Montana with troughing extending
southwestward toward Southern California. Impulses moving through
the flow with broad lift and deep moisture (axis of precipitable water in excess
of 1.5") with convection from the Southern Plains into the
The short range models are in good agreement with the closed low
opening up tonight as it shifts east into the
Dakotas...meanwhile...energy remains trailing to the southwest
eventually closing off over Nevada by 18z Tuesday. H85 warm
advection continues this evening...however is not as robust in our
area after 06z. Will maintain moderate to high pops this evening
with decent forcing and deep moisture of 10-15 deg c h85
dewpoints...however precipitation coverage focuses farther east as
the flow veers and the axis of high precipitable water air shifts east. Patches
of showers and isolated thunder continue overnight with mid and
upper level support...and better pops will be in southeast
Nebraska and southwest Iowa into Kansas and Missouri Tuesday.
Dewpoints in the 40s will work in from the northwest with 50s/60s
farther southeast. With light winds overnight and wet ground
should see some areas of fog. With the clouds...most models are
not hinting at vsbys less than a mile save for some patches in
Decreasing clouds later Tuesday as the soundings dry out from a
precipitable water of 1.6" at 00z today to 0.8" by 18z Tuesday at Omaha.
With surface high pressure over the area...will need to assess fog
again Wednesday morning.
Drier weather for Wednesday and Thursday. Cooler highs closer to
normal in the upper 60s to mid 70s each day
Long term...(thursday night through monday)
issued at 330 PM CDT Mon Sep 25 2017
The closed low pressure system over the southwest U.S. Lifts
north later this week and by Friday night and Saturday a few
showers or thunderstorms may try to sneak into the area. There is
a better chance for showers and thunderstorms later Sunday into
Monday. Highs remain in the 60s and 70s.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1150 am CDT Mon Sep 25 2017
Expect mainly IFR conditions at all three sites, with some tempo
MVFR conditions. Rain showers with some embedded thunderstorms and rain will make for a
messy taf forecast the next few cycles. Conditions should improve
at kofk toward 18z Tuesday, but probably closer to 00z Wednesday
for koma and klnk.