Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 090605

Area Forecast Discussion
National Weather Service Hastings NE
1205 AM CST Sat Dec 9 2017

Issued at 523 PM CST Fri Dec 8 2017

IR sat imagery shows substantial multi-layered altocu and
cirrostratus moving S associated with the upr-lvl jet. Fcst sky
coverage was increased substantially thru 06Z...then decreased as
multi-model cross sections show the axis of clds shifting E with
the jet max.

These clds will probably slow the temp drop this eve. Will monitor
and make adjustments as needed.


.SHORT TERM...(This evening through Saturday)
Issued at 226 PM CST Fri Dec 8 2017

The pattern aloft was highly amplified with an upper ridge along
the western CONUS, northerly flow across the Central Plains and a
trough to the east from Ontario south through the Great Lakes and
Ohio valley region. A cold frontal boundary crossed our region
this morning, and while cooling behind this boundary is not as
cold as a day ago, the cooler air across eastern Nebraska and
Kansas will hold temperatures down compared to locations to the
west. Temperatures will also feel chilly into the evening with the
gusty northwest winds.

Winds look to remain steady through the overnight hours which will
help hold temperatures in the 20s for lows. On Saturday, low cloud
cover looks to edge into our far eastern zones in the morning,
then clear out by afternoon and should not have much impact on
temperatures. Overall temperatures will be on the upswing as the
cooler airmass exits farther to the east with the departing upper
trough and warmer air advects onto the Central Plains in rising
heights as the western upper ridge builds east.

.LONG TERM...(Saturday night through Friday)
Issued at 226 PM CST Fri Dec 8 2017

The outer periods continue to feature dry weather and above normal
temperatures, with Sunday the warmest day of the extended forecast.

The airmass warms considerable on Sunday with mid level
temperatures averaging near 10C and guidance continues to trend
warmer with temperatures with highs averaging near or in the 60s.
These temperatures are well above normal when highs average in
the 30s and temperatures this warm are looking to be at least near
record highs.

Grand Island record high for 12/10/17: 66 degrees set in 1990

Hastings record high for 12/10/17: 64 degrees set in 1939

Agree with previous shift that Sunday will need to be closely
watched for fire weather concerns due to the warm, dry conditions
with steady west/northwest downslope winds. Wind speeds look to be
the strongest in the morning, then weaken during the afternoon as
the gradient relaxes, but it could be close to meeting fire weather
criteria if winds remain stronger during peak heating as low
relative humidity values are forecast to average 15 to 25 percent.

The super mild day on Sunday will be shortlived as a clipper system
sends a cold front south through the plains Sunday night and early
Monday. The cold frontal passage will be noticeable and accompanied
by strong and gusty northwest winds which will remain intense
through the day Monday. Model forecast soundings suggest mixing
will be above H85 with winds at the top of the layer forecast
between 45 and 50kts. Both the H7 and H850 winds average 1 to 2
standard deviations above normal and it`s shaping up to be quite a
windy day with wind gusts of 45 to 55 mph possible, similar to
last Monday and will mention the strong wind potential in the HWO.
Post frontal daytime temperatures will be cooler, averaging in
the 40s and 50s but in the still dry airmass, low relative
humidity values are forecast in the lower 20th percentile across
north central Kansas and our far southwest Nebraska counties and
will mention near critical fire weather conditions in the HWO.

The remainder of the extended remains dry with mild temperatures.
Tuesday is looking fairly nice with less wind in between systems.
Models show another cold frontal passage Wednesday, followed by
warming trend for the latter part of the week.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1204 AM CST Sat Dec 9 2017

General overview:
Confidence is very high in VFR visibility and precip-free weather,
and is high in VFR ceiling, with only the slightest concern for
MVFR at KGRI. Really, the main aviation issue will be two rounds
of low level wind shear (LLWS), one early this morning and another
late in the period Saturday night. Read on for more element-
specific details...

Winds (including LLWS):
Surface winds will actually be relatively light throughout, with
sustained speeds prevailing at-or-below 12kt from the west-
northwest the majority of the time, and any slightly higher gusts
mainly occurring Saturday afternoon. The bigger issue will be
LLWS, and have continued/introduced two rounds: 1) Have extended
the previously-advertised mention for early this morning through
12Z, as even though it`s fairly marginal, winds increasing to
around 40kt within the lowest 1,500 ft. could create up to around
30kt of shear magnitude between the surface and this level...2)
Very late in the period another, likely stronger round will
commence with winds in roughly the lowest 1,000 ft. increasing to
around 40kt, again setting up 30+kt of shear magnitude.

Although would be very surprised to see it reach as far southwest
as KGRI, it`s worth noting that some models are bringing an MVFR
ceiling within 60-80 miles northeast of there during the 12-18Z
time frame. While this obviously bears watching, confidence is
currently so low in this affecting KGRI that it will not even be
"hinted" at with a scattered low cloud mention.




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