702 
FXUS63 KLSX 161947
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
247 PM CDT Sun Oct 16 2022

.SHORT TERM...  (Through Late Monday Night)
Issued at 236 PM CDT Sun Oct 16 2022

Attention will be on the rather brief, but deep cold spill that is 
already underway. There is high confidence that a widespread hard 
freeze will occur Monday night into early Tuesday.

Regional surface analysis initially showed a stationary boundary 
stretching from the vicinity of the TN/KY border, westward through 
northern AR. Thicker cloud cover remnant of active weather aligns
in the general vicinity of the boundary with a few mid to high 
clouds extending north along I-70. A strong cold front is pushing 
through the forecast area from north to south, extending across
the southern section of the CWA just before 20z this afternoon. 
Surface flow has turned out of the northwest behind the front, 
marking the onset of cold air advection that will continue tonight
into Monday. 

Though today's diurnal heating potential was capped by the initial 
arrival of the surface front, the core of the cold air remains 
poised to move in on the north-to-south push within the mid-level 
flow late this evening into the overnight period. This will be 
supported by the deepening surface low over the Great Lakes Region 
in conjunction with a surface high building into the northern 
plains. Tonight's lows will be chilly with some area dropping
below freezing, mainly over central and northeast Missouri.
However, after collaborating with surrounding offices, it was
decides to refrain from frost freeze headlines with many of these
areas already hitting similar temperatures back on October 8th 
and multiple other nights near or just below freezing. 

By Monday, standardized height anomalies show height falls over 
the Great Lakes will peak between 3-4 standard deviations below 
normal, while height rises will reach 2-3 standard deviations 
above normal just west of the Hudson Bay during the day Monday. 
The anomalous tandem will act to jettison cold air southward, 
incorporating negative 15-20C at 850mb. Though it will moderate 
some by the time it reaches the mid-Mississippi Valley, it will 
spread negative 8-10C air across the entire forecast air with the 
0C isotherm (2+ standard deviation below normal) reaching near the
Gulf Coast by Tuesday morning, signaling just how strong this 
cold push will be.

The cold air will take hold with highs struggling to reach 50 
degrees and that's considering the warmest portions of the 
forecast area south of I-70. There is high confidence in a 
widespread hard freeze Monday night, strengthened by ensemble 
data with individual members clustering around the 50th 
percentile with lows in the 20s. The past couple forecast cycles
had NBM/NDFD forecasts generally been plotting in the 75th-90th 
percentile with overnight temperatures hovering around the 90th 
percentile. This suggests that we may still be a few degrees too 
warm. Therefore, updates have been blended with 50th percentile to
nudge temperatures slightly colder. Provided the high confidence
forecast, the freeze watch was upgraded to a freeze warning Monday
night into Tuesday morning. 


Maples

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 236 PM CDT Sun Oct 16 2022

Near-record cold will lead off the extended period. Temperatures 
begin to moderate through midweek before more substantial warmth 
returns later in the week.

A longwave upper trough will dominate the pattern over the eastern 
U.S., while upper level ridging extends northward through the 
Intermountain West. This supports the continued northerly feed 
throughout the Mississippi Valley with anomalously cold air 
remaining in place Tuesday into Tuesday night. Surface high pressure 
elongates southward just west of the Mississippi River with 
northerly flow persisting through MO/IL. The mid-level airmass only 
warms by a couple of degrees with negative 5-8C being fairly 
representative across the forecast area. Temperatures will remain 15-
20 degrees below normal with highs largely in the 40s and lows in 
the 20s. A few of the normally colder locations will likely see 
upper teens Wednesday morning with a second straight night of 
widespread freezing temperatures. 

Though Wednesday will remain well below normal, it will mark the 
beginning of a moderating trend. The upper level low over the 
eastern U.S. begins to shift slightly east as surface high pressure 
shift into the southern Plains and gulf states. Surface to mid-level 
flow begins to turn westerly but may only do so later in the day. 
This allows cooler air to hang on with highs getting around a 3-5 
degree boost. There is a weak upper level shortwave that quickly 
pushes north to south down the western side of the eastern trough 
late Wednesday. However, it looks to pass over unnoticed with little 
more than a temporary mid-level wind shift. 

A pattern shift occurs Thursday through the end of the period. The 
eastern CONUS upper low moves north and broadens over the Hudson Bay 
as the western ridge flattens with the arrival of another system 
along the coast of British Columbia. Thursday's north/northwesterly 
upper level flow gradually turns westerly Friday and eventually 
southwesterly heading into the weekend. The more sensible change 
will be supported by surface/mid-level ridge that builds from the 
northern gulf through the mid-Atlantic. Southwesterly flow 
strengthens around the northern periphery of this ridge Thursday 
through Saturday, feeding 15-20C air northeast out of the southern 
plains. Though there is some spread in the ensembles this far out, a 
majority of the member support 70s over parts of the are Friday. By 
Saturday and Sunday 70s are favored over much of the region with few 
ensemble members hinting at low-80s. 

Rainfall still looks to be at a premium with any potential coming 
late next weekend, if not early next week. An upper level trough 
deepens over the west and moves into the plains, potential giving 
rise to a surface low on the lee side of the Rockies. With plenty of 
time to go, far too much can change to have much confidence in how 
this plays out with regard to any beneficial moisture.


Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1240 PM CDT Sun Oct 16 2022

VFR conditions are expected to extend through the end of this TAF
cycle. Thicker mid to high clouds run along a stationary boundary
well to the south (AR/TN/KY) of all terminals. A few mid-level 
clouds over northern MO continue to erode as they encounter dry
air. Provided the sunshine between the two, deeper mixing will
result in an occasional afternoon gusts. Northwesterly winds will
be sustained between 5 and 10 knots tonight with a better 
potential for gusts from mid-morning Monday through the afternoon 
period. 

Maples

&&

.CLIMATE...  
Issued at 215 PM CDT Sat Oct 15 2022

                MON       TUE       WED
                17        18        19
STL--
    LOW MAX   49(1976)  42(1880)  42(1989)
    LOW MIN   29(1943)  27(1976)  25(1972)

COU--
    LOW MAX   48(1976)  38(1898)  41(1930)
    LOW MIN   26(1976)  25(1952)  22(1972)

UIN--
    LOW MAX   46(1989)  45(1989)  41(1989)
    LOW MIN   27(1943)  24(1948)  20(1972)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Freeze Warning from 9 PM Monday to 9 AM CDT Tuesday for Audrain 
     MO-Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln 
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte 
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

IL...Freeze Warning from 9 PM Monday to 9 AM CDT Tuesday for Adams IL-
     Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Pike IL-Randolph IL-Saint Clair-Washington IL.

&&

$$

WFO LSX