Forecast Discussion
NWS Omaha/Valley, NE

000
FXUS63 KOAX 220440
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1140 PM CDT Thu Sep 21 2023

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 325 PM CDT Thu Sep 21 2023

Key Messages:

 - Scattered showers and thunderstorms are expected to move into
   eastern Nebraska overnight tonight, with the threat of strong
   gusty winds, large hail (particularly southwest of a line from
   Seward to Beatrice), and lightning.

 - The Friday severe weather risk is conditional, depending on the
   strength of the capping inversion. However, if storms are able
   to develop, there will be the risk for severe wind gusts and
   large hail up to 2 inches in diameter.

 - Numerous severe thunderstorms are possible across the region
   Saturday afternoon and evening. All mode of severe weather will
   be possible.

 - Lingering showers and clouds will persist across the region
   through Monday, giving way to clear and dry conditions Tuesday
   through the end of the forecast period.

...TODAY AND TONIGHT...

12Z UPPER AIR ANALYSIS SHOWS A LONG WAVE TROUGH POSITIONED OVER THE
WESTERN CONUS WITH STRONG DIFFLUENT FLOW OVER THE ROCKIES AND HIGH
PLAINS. 500 MB ANALYSIS SHOWS AN EMBEDDED SHORTWAVE TROUGH ROUNDING
THE EASTERN SIDE OF THE LONGWAVE TROUGH AND IS EXPECTED TO EJECT OUT
INTO THE CENTRAL HIGH PLAINS THIS AFTERNOON. AT THE SURFACE, CURRENT
OBS SHOWS EAST/SOUTHEASTERLY WINDS AT 10 TO 20 MPH ACROSS THE
REGION. WHILE SOUTHEAST NEBRASKA AND SOUTHWEST IOWA WILL SEE HIGHS
IN THE LOW 80S, A COLD POOL LEFT OVER FROM MORNING CONVECTION SHOULD
KEEP TEMPERATURES IN THE 60S AND LOW 70S FOR PORTIONS OF NORTHEAST
NEBRASKA.

TONIGHT, WITH THE EJECTION OF THE AFOREMENTIONED SHORTWAVE TROUGH
AND MODEST LOW LEVEL MOISTURE WITH DEW POINTS IN THE 60S, SCATTERED
STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
PORTIONS OF CENTRAL NEBRASKA. THESE STORMS ARE EXPECTED TO GROW
UPSCALE AND RESULT IN A CLUSTER OF STORMS, POSSIBLE AND MCS, WHICH
WILL MOVE INTO OUR REGION FROM THE WEST. CURRENT GUIDANCE SUGGESTS
THE MOST LIKELY TIME FRAME THESE STORMS WILL MOVE INTO EASTERN
NEBRASKA WILL BE AROUND 11PM, WITH THE HIGHEST CHANCES OF RAIN BEING
BETWEEN MIDNIGHT AND 4AM. THESE STORMS WILL POSE THE RISK FOR STRONG
GUSTY WINDS AND SMALL HAIL, BUT THIS THREAT SHOULD REMAIN WEST OF US-
81, AS AREAS EAST OF THE HIGHWAY WILL HAVE LIMITED INSTABILITY WITH
THE DEVELOPMENT OF A STRONG CAPPING INVERSION ASSOCIATED WITH THE
NOCTURNAL BOUNDARY LAYER AND STRONG WARM AIR ADVECTION IN THE 850-
700MB LAYER.

...FRIDAY AND FRIDAY NIGHT...

SCATTERED SHOWERS (30-40%) ARE EXPECTED TO LINGER ACROSS THE REGION
FRIDAY MORNING, WITH RAIN ENDING BY 11AM. OVER THE COURSE OF THE
AFTERNOON, FLOW AT THE SURFACE IS EXPECTED TO VEER AND BECOME MORE
SOUTHERLY WITH THE DEVELOPMENT OF A SURFACE TROUGH ASSOCIATED WITH
THE EJECTION OF ANOTHER SHORTWAVE TROUGH INTO THE CENTRAL PLAINS.
THIS WILL ALLOW MODEST MOISTURE TRANSPORT INTO THE REGION FROM
THE SOUTH, WITH DEWPOINTS INCREASING TO THE MID AND UPPER 60S.
HOWEVER, EVEN THOUGH THERE IS SUFFICIENT LOW LEVEL MOISTURE AND
SUBSTANTIAL DYNAMIC FORCING THAT WILL MOVE INTO THE REGION
TOMORROW AFTERNOON, A STRONG FLOW (25-40 KNOTS) IN THE 850-700 HPA
LAYER WILL ADVECT WARM AIR INTO THE REGION FROM THE
SOUTH/SOUTHWEST. THIS WILL HELP REINFORCE THE CAPPING INVERSION
OVER THE COURSE OF THE DAY, CREATING A CONDITIONAL RISK FOR STRONG
TO SEVERE THUNDERSTORMS ACROSS NORTHEAST NEBRASKA. IF FLOW IN
THIS LAYER TAKES ON A MORE WESTERLY COMPONENT, STORM INITIATION
MAY BE INHIBITED ALTOGETHER ACROSS THE REGION. IF FLOW IN THIS
LAYER TAKES ON MORE OF AN EASTERLY COMPONENT, WARM AIR ADVECTION
WILL BE WEAKER CONTRIBUTING TO A WEAKER CAPPING INVERSION AND
ALLOWING MORE GREATER COVERAGE OF STORMS LATER IN THE EVENING AND
OVERNIGHT HOURS. WITH ANY STORMS THAT DEVELOP, LARGE HAIL AND
STRONG DAMAGING WINDS WILL BE THE PRIMARY HAZARD, BUT A TORNADO
CANNOT BE RULED OUT.

...SATURDAY AND SATURDAY NIGHT...

THE LONGWAVE TROUGH OUT WEST IS EXPECTED TO EJECT INTO THE
NORTHERN PLAINS SATURDAY AFTERNOON. THIS WILL CONTRIBUTE TO THE
DEVELOPMENT OF A SURFACE LOW IN CENTRAL SOUTH DAKOTA THAT WILL
TRACK TO THE NORTHEAST, AND A SECONDARY LOW WHICH IS EXPECTED TO
DEVELOP ACROSS NORTHEASTERN KANSAS. AT THE SURFACE, A DRY LINE IS
EXPECTED TO DEVELOP IN CENTRAL NEBRASKA AND MIX EASTWARD INTO THE
REGION DURING THE AFTERNOON HOURS. AHEAD OF THE DRYLINE, SURFACE
DEW POINTS WILL BE IN THE 60S, WITH TEMPERATURES REACHING INTO THE
80S. THIS WILL ALLOW FOR MODEST INSTABILITY TO OVERSPREAD THE
REGION, WITH MLCAPE 1000-2000 J/KG. UNLIKE FRIDAY, THE CAPPING
INVERSION IS EXPECTED TO WEAKEN ALLOWING FOR THUNDERSTORM
DEVELOPMENT ALONG THE DRYLINE BY 4PM. WITH CROSS BOUNDARY FLOW,
BULK SHEAR 40-50 KNOTS AND 0-3KM SRH BETWEEN 200 AND 300 M^2/S^2,
A LINE OF SUPERCELLS APPEARS PROBABLE WITH ALL MODES OF SEVERE
WEATHER POSSIBLE. THERE IS STILL UNCERTAINTY WITH HOW FAR WEST
THESE STORMS WILL DEVELOP, BUT MODEL CONSENSUS IS THAT A LINE OF
STRONG TO SEVERE THUNDERSTORMS WILL DEVELOP BY THE TIME THE DRY
LINE REACHES THE MISSOURI RIVER. STORMS SHOULD BE EAST AND SOUTH
OF THE REGION BY MIDNIGHT.

...SUNDAY THROUGH THURSDAY...

THE WEEKEND STORM SYSTEM IS EXPECTED TO BECOME CUTOFF AND LINGER
IN THE NORTHERN PLAINS/UPPER MIDWEST THROUGH MONDAY NEXT WEEK.
THIS WILL BRING CLOUDS AND SCATTERED LIGHT RAIN SHOWERS TO
PORTIONS OF NORTHEAST NEBRASKA AND WESTERN IOWA. BY TUESDAY THE
SYSTEM SHOULD MOVE EAST OF OUR AREA BRINGING CLEARER AND DRIER
CONDITIONS TO THE REGION FOR THE END OF THE FORECAST PERIOD.
TEMPERATURES DURING THIS TIME ARE EXPECTED TO BE AVERAGE, WITH
HIGHS IN THE MID AND UPPER 70S AND LOWS IN THE LOW 50S.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1137 PM CDT Thu Sep 21 2023

VFR conditions at TAF issuance, but MVFR conditions potentially
developing by 10-12z, then back to VFR by 22z at KLNK/KOMA and 23/04z
at KOFK. We`ll also have to contend with shower and thunderstorm
chances early in the TAF, the best chance for thunderstorms
appears to be be at KLNK 08-10z, and KOMA 10-12z. There may also
be spotty showers in the clouds Friday afternoon into the evening,
but too far out to reliably forecast at this time. Southeast
winds generally less than 12 knots through the period.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

DISCUSSION...Darrah
AVIATION...DeWald

NWS OAX Office Area Forecast Discussion

Forecast Discussion
NWS Hastings, NE

000
FXUS63 KGID 220517
AFDGID

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
1217 AM CDT Fri Sep 22 2023

.UPDATE...
Issued at 1214 AM CDT Fri Sep 22 2023



UPDATE Issued at 956 PM CDT Thu Sep 21 2023

The tornado watch for portions of south central Nebraska and north
central Kansas has been allowed to expire. while the threat for
tornadoes has diminished, a few strong to marginally severe
thunderstorms remain possible early this morning. The main
hazards with the stronger storms will be strong winds and heavy
rainfall, which may result in localized flooding.

&&

.DISCUSSION...(This evening through Thursday)
Issued at 133 PM CDT Thu Sep 21 2023

Key Messages:

* Thunderstorms chances the next 48 hours or so are main focus of
  the forecast, and to what extent the area could see severe
  weather.

* The forecast returns to "mostly dry" in the mid/longer period
  with temperatures at or slightly above seasonal normals.

Deck of low/mid level clouds across the forecast in response to
deep moisture return and warm advection ahead of western US trough
and lead shortwave moving in Colorado region. Surface dewpoints
"up there" for late September...well into the 60s. With the clouds
have come scattered showers and cooler temperatures, especially
across the northern forecast area which has had an outflow from
morning thunderstorms in northeast Nebraska move through.

Tonight the issue is thunderstorms, coverage and severity. The
bottom line is there is uncertainty in both coverage and intensity
but also enough "juice" to support some strong/severe storms for
a time. First, the mid-level showers may perk up a bit as they
move northeast across the areas the next 3-4 hours. Not looking
for severe weather but a strong storm or two southeast of Hastings
is possible. The main severe risk initially appears to be just
west of the forecast, in southwest Nebraska on the lead edge
of the deep moisture and differential heating. Initial storm
development there could be severe in the later afternoon, but
development farther into southern Nebraska in the 6 to 9 pm
timeframe appears probable. This convection has the potential to
produce large hail and strong winds. Some, discrete supercell in
the early evening will be worth watching for a tornado, but
personally think that is more likely just west. By mid/later
evening, a decent low level jet will promote more development and
sustainability to the east across much of the forecast area it
appears. Again, severe storms possible, but overall severity
should wane toward midnight. Should the storms develop in this
manner, there will be some decent rain to measure in a few
people`s rain gauge.

The upper level low and and main front move through on Saturday
morning. Prior to that, rain/storm chances Friday favor north of
the forecast area. Although we display 40-50% rain chances north
of I-80 tomorrow night, I think that may be too high. Same vote
for Saturday, as the frontal timing and proximity of the low don`t
suggest real great rain chances. Expect to see those chances
tighten up and decrease Saturday in the east. Temperatures will
drop a bit behind the front (from early this week) but still hold
around normal for the weekend.

Unfortunately, time has been sparse to look much at the longer term
part of the forecast...roughly Sunday through Thursday. In
general, an upper level ridge aloft will temporary assert itself
for a few days keep much of the area mainly dry. Having said that,
there small chances for showers/isolated thunderstorms. One is in
the eastern areas Monday/Tuesday. Those are tied to the weekend
upper low sort of shearing apart over eastern NE/IA. Pretty big
assumption at this point and I would not be surprised if those
eventually disappeared. And I would not bet too much on the rain
chances later in the week just yet either. There is a LOT more dry
than wet next week. Temperatures will be normal to slightly above
normal (normal highs next week 73-79 degrees)which has been the
trend much of September. And with morning lows in the lower/middle
50s, that is a pretty pleasant week for the first full week of
autumn. Lighter winds early in the week will pick up and becoming
more steady about midweek ahead of the potential trough by next
weekend.



&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1144 PM CDT Thu Sep 21 2023

-SHRA expected to end early this morning and behind the rain
 models bring in some IFR ceilings. The winds have been a little
 squirrely from the storms, but should become more easterly once
 this wave moves out. The models still vary in timing of lifting
 of ceilings so kept with afternoon timing for ceilings to lift.
 Some models hold the IFR ceilings all day. With all of the precip
 tonight, I would expect BR/FG Friday evening, so put 6BR to start
 off the potential for FG in future TAFS.



&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

$$

UPDATE...Wekesser
DISCUSSION...NOAA/NWS/Moritz
AVIATION...Beda

NWS GID Office Area Forecast Discussion