National Weather Service Raw Text Product

511 
FXUS63 KDMX 210528
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1128 PM CST Mon Nov 20 2017

...Updated for 06z Aviation Discussion...

.SHORT TERM.../Tonight through Tuesday/
Issued at 324 PM CST Mon Nov 20 2017

A cold front will enter northwest Iowa by 06Z this evening and push 
through the state by 12Z Tuesday morning.  High pressure at the 
surface will build into the state for the rest of the day. Aloft, a 
pretty strong shortwave will swing through the state.  A narrow area 
of lift will accompany this shortwave moving across northern Iowa in 
the morning then dropping through the eastern third to half of the 
state for the rest of the day.  Strong winds will will occur behind 
the front and will be enhanced as this area of lift drops across 
northern then eastern Iowa.  Winds post frontal will increase across 
northern Iowa to 15g25kts by or shortly after 09z then increase with 
that area of lift to around 30g40kts for about a 4 to 6 hour window. 
Pretty high confidence that northern Iowa will see borderline to 
advisory criteria wind speed/gusts.  So as a result will issue a 
wind advisory for northern Iowa from 12Z to 19Z.  As the shortwave 
quickly passes east the area of lift mainly grazes the eastern third 
or so of the state and while winds will likely increase, confidence 
is somewhat less that we will see advisory criteria.  Winds will be 
hit hard in the forecast and HWO but the advisory can be expanded 
with later shifts as confidence grows.  Moisture is woefully lacking 
with this system so other than some mid/high clouds we will not see 
precip...just wind and cold.

Regarding temps...we will be in strong cold advection during the day 
Tuesday so expect highs to be some 20 to 30 degrees colder than 
today. 

.LONG TERM.../Tuesday night through Monday/
Issued at 324 PM CST Mon Nov 20 2017

Little change to trends over the next 7 days. Cold conditions will 
persist Tuesday night as ridge of high pressure passes across the 
state. Overnight lows will dip into the mid to upper teens at most 
locations. Warm advection will arrive by Wednesday afternoon as the 
high pressure system moves east and low pressure enters the Dakotas. 
Despite the warm advection Wednesday, temperatures will remain cool 
with highs in the mid 30s to lower 40s. Much warm temperatures 
arrive for the end of the week as the thermal ridge arrives with 
highs in the 40s and 50s Thursday and the 50s and 60s on Friday. An 
inversion around 900 mb Thursday will keep the temperatures cooler 
despite very warm temperatures aloft followed by deeper mixing on 
Friday. A few things of note on Friday. Guidance is trending a 
little faster with a boundary entering at least northern Iowa by 
Friday afternoon. Associated clouds associated with the boundary 
will have an impact on temperatures. The initial cold advection 
though should be countered by deeper mixing with the frontal passage 
with the stronger cold advection arriving Friday night. If the sun 
persists over central and southern Iowa into Friday afternoon, then 
forecast highs may still be too low and may approach record highs.

Guidance is trending farther east with the long wave trough over the 
weekend which would keep Iowa a little warmer over the weekend 
though still much cooler than Friday. Ridging will begin to move 
back into the region early next week that will bring a return to 
near to above normal temperatures by Monday. Little to no 
precipitation is expected through the forecast period.

&&

.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1128 PM CST Mon Nov 20 2017

Winds have dropped off to between 5 and 10 knots this evening at
the terminals. However, winds will increase as a cold front 
currently over the far northwest part of the state moves through
the state the rest of the night into tomorrow morning. Gusty 
winds from the northwest will develop with gusts of 25 to 35 knots
common after the front's passage. Clouds will accompany the front
and did lower bases a few to several thousand feet from previous 
forecast, but still well within the VFR range. Forecast soundings 
and cross sections do continue to show increasing low level 
moisture over the northern TAF sites as moisture wraps around low 
pressure well north of the area. Therefore, did add some SCT035 
and SCT040 ceilings at KMCW and KALO, respectively, to account for
the possibility of these lower cloud bases in this TAF issuance. 
Otherwise, as the low pressure and cold front move farther away in
the afternoon, VFR conditions should prevail.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 6 AM to 1 PM CST Tuesday for IAZ004>007-016-
017.

&&

$$

SHORT TERM...FAB
LONG TERM...Donavon
AVIATION...Ansorge