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FXUS63 KGID 231111 AFDGID

AREA FORECAST DISCUSSION National Weather Service Hastings NE 611 AM CDT Sat Sep 23 2023

Aviation Update

DISCUSSION
(Today through Friday)
Issued at 350 AM CDT Sat Sep 23 2023

Key Messages:

* Areas of fog and severe thunderstorms (two things you don't often hear mentioned in the same sentence!) will impact portions of mainly south central Nebraska this morning.

* Much quieter conditions return for the afternoon, though the warm and breezy conditions could yield elevated fire weather conditions in Furnas and Rooks Counties.

* Seasonably mild/warm temperatures and dry conditions are forecast for the remainder of the weekend and most, if not all, of next week.

Forecast Details: Main weather impacts this forecast period will come right off the bat this morning in the form of fog (potentially dense on an isolated/brief basis), and severe thunderstorms for portions of south central Nebraska. All of this will occur ahead of a W to E moving sfc front that is associated with a potent upper level trough currently seen on WV imagery spinning over WY.

Potential for severe t-storms is first and foremost concern this morning. Already have some very robust convection that has developed along the front over the past hr W of LBF, which is a little bit sooner and further S than what most hi-res models had last eve. I think this speaks to the strong lift associated with ejecting mid level speed max (60-70+ kt at H5) and robust low level moisture and instability already in place ahead of the front.
Latest SPC mesoA page shows a large reservoir of 2000-3000 J/kg MUCAPE that is generally co- located with 40-50+ kt of effective deep layer shear. This CAPE/shear parameter space is more than sufficient to support supercells with up to golf ball size hail.
This activity is also developing in environment of very steep mid level lapse rates of 8-8.5 C/km, further supporting notion that large hail will be likely in strongest storms. Thus, its no surprise that the sig hail parameter is as high as 2-3 ahead of this line - which is quite impressive not only for this time of day, but also for late Sept. Forecast soundings for places like LXN to ODX show deeply saturated low levels beneath steep mid level lapse rates and dry air - which supports the high MUCAPE, but also very stable near sfc layer. Think this should limit the severe wind potential until storms progress E of the CWA and BL has time to start to mix. So, in summary, expectation is that a line, or broken line, of at least strong storms to move W to E across portions of south central NE this morning, particularly along/N of I-80. Would also bet some of these will be severe, as well, and pose a risk for quarter to golf ball size hail - particularly between about 6AM to 8/9AM.

As for the fog potential...far W/NW portions of CWA have reported some vsbys around 1 mi, or less, over the past couple of hours...and expect this to continue, if not expand, as moisture continues to increase/pool ahead of the front. This front will act as a broom to sweep it across the area this morning - so significant vsby fluctuations will certainly be possible. However, the front will also help to scour out the fog/low clds behind its passage as drier W/NW flow moves in. Thus, due to the expected iso-scat coverage and transient nature of any dense fog, the need for any formal headline appears low at this time, but have continued mention in the HWO.

The rest of the forecast appears to be about as quiet and comfortable as one could ask for in late Sept - cool nights and warm days. The overall upper pattern looks to become pretty stagnant next week, due in large part to a strong, blocking high pressure over the Hudson Bay area in Canada. Positive height anomalies also appear probable over the Desert SW - with at least some phasing in between these maxima expected broadly over the central Plains. Latest EPS probs for measurable pcpn in any 24 hr period is about 10 percent or less until at least late next week or next weekend. Ensemble spread in max/min temps is also very low, suggesting overall high confidence/predictability that a prolonged stretch of dry weather and pleasant temps will indeed pan out next week. Highs will start off the week in 70s/80s, before 80s/90s become more likely for second half of the week.
Latest NBM suggests 70-90+ percent probabilities for highs above 80 deg for entire CWA Wed thru Fri. Lows will start off the week in the 40s or 50s before warming to mostly 50s to low 60s later in the week. For reference, avg highs/lows for late Sept are generally in the mid-upper 70s and mid 40s to low 50s, respectively.

AVIATION
(For the 12Z KGRI/KEAR TAFS through 12Z Sunday)
Issued at 610 AM CDT Sat Sep 23 2023

Significant weather: IFR to LIFR CIGs, and MVFR to IFR VSBYs until mid morning.

Today: Low clds and fog will overspread the terminals early this morning ahead of a front moving in from the W. Expect ceilings around 400-900ft and visibilities around 2-5sm within this stratus deck. Could also see some iso-scat shwrs/storms in the 12Z to 15Z time frame as well, though greatest chances/coverage is forecast to remain N of the terminals. With the passage of the front will come veering winds from S to WNW/NW, again in that 14Z to 16Z time frame from W to E. Brzy conditions will settle in behind the front with sustained speeds 10-14kt, and gusts 20-25kt. Drier air will lead to decr clds and return to VFR by midday. Confidence: High.

Tonight: VFR conditions with light NW to W winds 5-9kt likely.



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

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