National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-12-06 09:38 UTC


064 
FXUS63 KDMX 060938
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
338 AM CST Thu Dec 6 2018

.SHORT TERM.../Today through Tonight/
Issued at 338 AM CST Thu Dec 6 2018

Key Points: Cloud cover and temperatures were the main focus today 
into tonight. 

Cold front has nearly cleared the southeast portion of the Iowa 
early this morning with a secondary front draped across central 
Minnesota and across the Dakotas.  Very large surface high pressure 
progged to move into the state today and become centered over the 
forecast area by tonight.

The biggest question is whether or not this stratus deck erodes and 
remains clear by tonight or continues/redevelops with the sunshine 
today. Latest IR satellite trends appear that the stratus is trying 
to break up across portions of central and southern Minnesota and 
parts of South Dakota and then the high cirrus deck over Iowa 
shielding the low stratus deck underneath and uncertain on the 
stratus deck breaking up other than a very sporadic observations.  

Leaned toward the clearer skies tonight with the GFS bufr forecast 
soundings suggest no inversion tonight, or at least a very weak one 
depending on the location. The NAM is more bullish in developing the 
inversion and bringing in low level moisture by Friday morning, 
especially across the west and suggesting the cloud cover to return. 
Thus, the MOS guidance via NAM is much warmer than the GFS. The ARW, 
RAP, and even the NMM bring in some low stratus across far western 
Iowa into eastern Nebraska and parts of South Dakota by around 06-
09z Friday. Certainly a hint of the stratus returning and in some 
agreement with the NAM.  Challenging temperature forecast, for both 
the max today and min tonight as they are be highly dependent on 
cloud cover dissipating, returning, or not returning and also if it 
does return, how widespread.  Leaned toward the cooler MAV guidance 
for today as fairly confident the cloud cover will remain across the 
forecast area through at least midday and even into the early 
afternoon. Then tonight, a slight lean toward the cooler side of 
guidance, especially over the west and north where the should be 
clear skies and light winds this evening with the surface high 
overhead.  However, with some of the guidance bringing back in cloud 
cover towards Friday morning, could see some steady or even rising 
temperatures overnight depending on how much they drop off prior to 
the cloud cover returning. High confidence this high pressure is 
bringing a very cold airmass into the state, low confidence in the 
cloud cover forecast.  All said and done, there is a high potential 
for portions of the forecast area to be either too warm or too cold 
or both wrt the forecast minimum temperature.

.LONG TERM.../Friday through Wednesday/
Issued at 338 AM CST Thu Dec 6 2018

/Friday through Monday/...

Confidence: High

Main concerns early in the period will be extent of warming aloft 
and eventual sfc response. As speculated in the previous two nights,
some clouds will already be entering northern Iowa in response to
a warm front and frontal zone nearing the northern portion of 
Iowa early Friday morning. This should limit overnight lows from 
getting too far below zero north while Friday afternoon highs may 
also be held back a few degrees across the north. Winds appear to 
remain either light or out of the west northwest most of the day 
as an area of high pressure parks itself over the state through 
00z Saturday. Though minor, there are some differences between the
Euro and the GFS with the Euro a degree or so colder at H850. 
H850 temps of -9C northeast to -6C southwest compared to the GFS 
is -8C to -6C southwest. This should allow afternoon highs to 
reach the lower 20s northeast to the mid to upper 20s south. By 
06z Saturday, the high drifts a bit east of the region while 
another area of sfc high pressure develops over the Central Plains.
Aloft, we remain in split flow through the weekend. 

The southern stream continues to be more active and nearly every 
wave in the next 5 to 8 days will remain either south of our area 
or deepen once the wave passes east of our area. Overall, there is
a mean ridge of high pressure at H500 over the Northern Hemisphere 
and the large scale pattern favors continued less active weather 
across the Central/Northern Plains while more active weather is 
favored over the south/southeast and eastern CONUS. Saturday will 
likely moderate a few degrees as H850 temps warm. This trend will 
also continue into Sunday with both days featuring mid 20s to 
lower 30s for afternoon highs. On Sunday there is a closed low 
expected to track across Iowa at H500. Though generally moisture 
starved, it should bring a few clouds to the region during the 
daytime hours. Current forecast lows for early Monday morning will
be a challenge with high pressure nearby and possible cloud cover
as well. Though present lows are in the single digits over western
/northern Iowa, some upward revision may occur in the next few 
days. By Monday both the GFS and Euro show a return of southwest 
flow with warming at H850. Highs should rebound into the 20s to 
upper 30s over the region. 

/Monday Night through Wednesday/...

Confidence: Medium

There is general agreement in the pattern evolution between the 
GFS/Euro on Days6 and 7 with the exception of timing.  Both models 
show lee side trough development with an elongated trough passing 
through the area Wednesday and a system tracking through the southern
stream. The GFS is slightly faster with the trough arrival and 
the Euro has a more amplified southern stream. It's likely that 
clouds and some light precipitation will accompany the system 
sometime around Wednesday or Thursday. Specific details on precipitation
type and overall coverage are limited at this time. One similarity
for now is that any significant storm development will take place
in the eastern CONUS where upper level support favors storm deepening.
Highs Tuesday into Wednesday should remain in the 20s and 30s with
possible 40s at times. 


&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1122 PM CST Wed Dec 5 2018

Made notable changes to CIGs in this update. Broken stratus with 
bases near 1500 ft to 2500 ft have made it into northern Iowa,
impacting KFOD, KALO, and KMCW. Satellite shows these clouds
extending back into North Dakota, so am thinking they will persist
in some form into Thursday afternoon.

Timing of departure will likely need to be adjusted in subsequent
updates.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Podrazik
LONG TERM...REV
AVIATION...Kotenberg