Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/03/19

Area Forecast Discussion

National Weather Service Hastings NE

 954 PM CDT Wed Oct 2 2019

...Short Term Update...

.UPDATE...
Issued at 953 PM CDT Wed Oct 2 2019

Regarding the overnight hours/Frost Advisory situation:

THE BOTTOM LINE:
Have added Greeley County to our going Frost Advisory (valid 3-9
AM Thursday), which now means we have 5 of our far northern /west-
central Nebraska counties included.

MORE DETAILS:
As outlined well by preceding day-shifter below, tonight`s frost
potential is not a "slam dunk", but is instead somewhat
marginal/uncertain in nature. That being said, we do not want to
"miss" the first first possible frost of the fall, so we are
erring on the side of caution, if anything.

Essentially, have maintained a mention of "patchy frost" and
issued/maintained the Advisory for all counties where widespread
lows as cold as 35-37 degrees are expected. Possible mitigating
factors that could work against frost formation include:
lingering pesky/at least scattered low clouds, and northerly
breezes that are not truly calm (perhaps remaining up in the 4-8
MPH range).

Whether or not any frost actually forms early Thurs AM in our
northern/western zones, one thing we are confident in is that we
will NOT see sub-freezing temps of 32-or-colder, so this is NOT a
true freeze situation.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 150 PM CDT Wed Oct 2 2019

Aloft: RAP tropopause analyses and aircraft wind data cont to
show a moderately-amplified longwave pattern. An anomalous 594 dm
subtropical high was over the Ern USA....centered over the TN Vly.
A trof remained over the W...with a low over MT/WY. This low will
move E along the US-Can border tonight and then begin to weaken N
of the GtLks tomorrow. In its wake...heights will rise over the
Plns with a low-amplitude shrtwv ridge developing. Meanwhile...the
next trof will move onshore in the W.

Surface: A strong quasi-stationary front extended from the Srn
GtLks acrs KS into CO...with a couple weak lows migrated E along
it. Strong high pres was over ON. One of these lows will become
dominant over IL/IN tonight...forcing the front into the Srn Plns.
Anticyclogenesis will occur over the Cntrl/Nrn Plns with 1028 mb
developing. The axis of this high will drift acrs NEB/KS tomorrow.

Rest of this afternoon: Mostly cldy. Cld bases are lifting and
will cont to do so from W-E. Patchy drzl was roughly confined to
the E 1/2 of the CWA as of 1845Z. That drzl will come to and end
as cld bases rise. Some breaks in the OVC should develop W of Hwy
183.

Tonight: Gradual clearing and cold. This will be the coldest
night of the fall thus far. Patchy fog and possibly some patchy
frost from LXN-ODX. There could be some stratus that lingers from
GRI N and E...even past midnight.

Cold! Lows will be svrl degs below normal which we haven`t seen
much of since Sep 1.

Frost: Decided to keep the Advisory as posted from the 4 AM
shift... but am not excited about frost potential and confidence
in verifying is not high. Despite temps dropping into the 30s...
widespread stratus has lingered thru much of the day...and
probably will linger into the evening in some locations. Unless
there is decent decrease in dwpts/dry air advection...clearing in
the presence of lingering low-lvl mstr is more likely to result in
fog formation. The latent heat release would keep temps up just
enough to preclude frost.

The issue is the character of the fog. Predicting how widespread
and thick fog might be is very difficult in most situations. Given
that the fog could be patchy or confined to some areas and not
others...that might allow for a little frost to occur where fog
does not.

One other negative factor is the winds will remain 4-7 kt as
times.

So...decided to keep the Frost Advisory but change/decrease the
fcst wording from areas to patchy. It won`t hurt to cover
sensitive vegetation W-NW of the Tri-Cities...just in case.

Thu: Any patchy fog in the AM will rapidly dissipate. Should be
sunny or mostly sunny. GFS and NAM RH cross sections suggests
there could be a some patches of altocu moving in from the SW. A
very nice day with low dwpts and light winds.

There is a quite a diff between GFS and NAM MOS for high temps.
GFS has 62F at GRI while the NAM has 53F since it hangs onto low
clds longer. Did not go as warm as the GFS but certainly favored
the warmer side of the guidance envelope.

.LONG TERM...(Thursday night through Wednesday)
Issued at 150 PM CDT Wed Oct 2 2019

Aloft: The longwave pattern that has dominated the CONUS over the
last 30 days will finally break down. The Wrn trof is fcst to
retrograde into the E Pac for a time...allowing a ridge to build
over the Wrn USA with a trof in the E. There are diff`s in the
5-10 day time frame between the EC and the GFS/CMC ensemble means.
The EC hangs onto the Wrn ridge a bit longer...whereas the
GFS/CMC means bring the trof back into Wrn Can and the NW USA.

As far as the shorter wavelengths...the shrtwv ridge will depart
NEB/KS as the deep trof moving into the W tomorrow conts E. This
trof will cross NEB/KS Sat followed by a weaker trof Sun. Once
this trof exits to the E...the flow will shift to WNW or NW Mon-
Tue as the ridge builds. Sig mdls spread dvlps over the E Pac and
Wrn USA Tue.

Surface: Fri high pres will strengthen as it heads into the
GtLks. Meanwhile...a cool front associated with the Wrn trof will
be progressing E. A low is fcst to form over WY Fri night and move
E along the SD-NEB border. This should force the cool front
(currently over KS) to lift back N as a warm front...but the cool
front moving thru the Wrn USA will quickly follow and cross the
CWA Sat AM. High pres will strengthen to about 1034 mb over the
Wrn USA and slip SE onto the Plns Mon. This high will then head
into the Ern USA Tue with modified return flow here.

Temps: remaining cooler than normal...espcly during the daytime
hrs. Some days will be much cooler than normal.

Rain: Fri into Fri night is the next chance for shwrs/tstms. A
few shwrs could linger into Sat AM. Then dry. Instability will be
minimal with the Fri system. So no strong or svr tstms are
expected.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday)
Issued at 725 PM CDT Wed Oct 2 2019

General overview:
MVFR ceiling to prevail at least these first few hours, but rather
high confidence in VFR through the majority of the period, along
with precipitation-free conditions. There is the slightest chance
of brief MVFR visibility in light fog especially a few hours
either side of sunrise, but have only "hinted" at this with a "6SM
BR" mention. Winds will not be much of an issue, with sustained
speeds under 10KT the vast majority of the time, as direction
prevails northerly through most of the period before turning more
easterly late Thursday afternoon. Read on for more details
regarding ceiling trends...

Ceiling trends:
Based on satellite trends, stubborn MVFR stratus is going to be at
least slightly slower to scatter out than previously advertised
(especially at KEAR). Am still a bit concerned that we may be too
optimistic with timing, but have aimed for a 04Z return to VFR at
both terminals (medium-confidence). Even after scattering of the
low cloud deck does occur, cannot rule out at least brief/fleeting
return of MVFR through the late-night hours. Overall though,
especially the latter half of the period for Thursday daytime
carries fairly high confidence in VFR under mostly clear skies.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Frost Advisory from 3 AM to 9 AM CDT Thursday for NEZ039-040-046-
     060-061.

KS...None.
&&

$$

UPDATE...Pfannkuch
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Pfannkuch