Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 220806 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Hastings NE
306 AM CDT Fri Sep 22 2017

.SHORT TERM...(Today and Saturday)
Issued at 300 AM CDT Fri Sep 22 2017

An area of surface low pressure currently over western Nebraska
is forecast to move to the northeast into South Dakota. Behind
this, we will be left with a weak dryline and subtle wind shift
stretching across west-central Nebraska. This means another very
warm day for the region with high temperatures in the 90s. Winds
should gust to around 30 to 35 MPH during the afternoon for most
of the area. The good news is that increased moisture should keep
us from reaching critical fire weather conditions in our CWA, but
still may be near-critical along and west of a line from
Lexington to Stockton (RH in the 20 to 25% range and wind gusts 30
to 35 MPH).

By late afternoon, the HRRR and NAMnest are developing scattered
diurnally-driven thunderstorms along the aforementioned boundary.
This should be west of a line from Cambridge to Greeley. With 30
to 40 kts of bulk shear, there is a marginal risk for severe
weather, but low-level moisture will be a limiting factor. Without
much upper-level support, I expect that any thunderstorms will
start to wane by late evening and re-focus across northern
Nebraska and South Dakota along the edge of an increasing 850mb
low-level jet.

Heading into Saturday, a strong upper-level cutoff low will start
to push eastward across the Rockies. This will start to impart
some upper-level forcing into our area as well as gradually nudge
a surface cold front closer to the area. This will make rain and
thunderstorms likely across western and northern parts of the CWA,
but will take until at least Sunday before most of the CWA sees
appreciable precipitation.

.LONG TERM...(Saturday night through Thursday)
Issued at 300 AM CDT Fri Sep 22 2017

The long term forecast is dominated by widespread rainfall
expected Saturday night through Monday evening, followed by cooler
and mainly dry weather Tuesday through Thursday.

Well advertised, multi-day rain event still appears on track
although its progression eastward across the forecast area is
methodical. Its all about high rain chances from Saturday night
through Monday, just gradually spreading east. Best shot for rain
from Highway 281 west is Saturday night through Sunday night. Most
likely rain chance from Highway 281 east is Sunday night and
Monday. Several models show multi-inch rainfall totals and we area
currently forecasting rain amounts ranging from 1.50" in Mitchell
and Jewell counties, to nearly 3" in Valley county. The western
half of the area still appears to be the most likely area for
heavier rain amounts although developing a secondary southwest to
northeast rain axis further east not uncommon and certainly
possible. Localized 4"+ rainfall is possible with feed of moisture
into the region (2+ standard deviations above normal precipitable
water), but even with the heavy amounts, recent dry weather and
the slower nature of the rainfall should keep flooding concerns
minimal (if any) at most.

The slow moving surface front doesn`t really make great progress
until later in the day Sunday, which keeps the best rain chance
along or behind the front. Some MUCAPE along and ahead of the
front warrants T-storm chance, but sketchy mid-level lapse rates
averaging about 6 deg. C/KM should keep strong storm risk at bay
and coverage more isolated. Obviously the extreme warmth leading
up to this event will be squelched with the copious cloud cover
and expected rainfall with highs in the 60s for some areas Sunday
and Monday.

Have gone with a dry forecast for Tuesday through Thursday in the
wake of the main upper trough. ECMWF is settling more of cut off
system in the intermountain west and all the models are consistent
to some degree with surface pressure moving across the Central
Plains. Believe this trend will result in mainly dry conditions
with low dewpoints, cool mornings and afternoon temperatures
roughly 5-7 degrees below normal, but still some pleasant early
fall weather.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1213 AM CDT Fri Sep 22 2017

South winds may continue to gust to around 20kts at times through
the early morning. Even stronger winds 1000-2000 ft above the
surface around 50 kts will create a LLWS threat until shortly
after dawn.

Southerly winds increase again on Friday, eventually gusting to
around 30kts during the afternoon.

There is a slight chance for a few thunderstorms to approach EAR
from the west late Friday afternoon and evening, but confidence
is too low to include in the TAF for now.




SHORT TERM...Mangels
LONG TERM...Moritz
AVIATION...Mangels is the U.S. government's official web portal to all federal, state and local government web resources and services.