Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201823

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
123 PM CDT Sun May 20 2018

.SHORT TERM...(Today and tonight)
Issued at 245 AM CDT Sun May 20 2018

Regional satellite imagery continued to note a very elongated
circulation across the Central Plains, and portions of the Upper
Midwest. Elevated instability generated a few storms along the
Iowa border after midnight as the cold pool of one of the
circulations rotated across northern Iowa.

Although precipitation chances and amounts will be low over the
next 24-36 hours, several of the weak circulations will slowly
rotate across the plains and into the western Great Lakes through
Monday. Thus, will continue low chances of precipitation across
mainly far southern Minnesota, and into west central Wisconsin.
Temperatures will remain in the 50s and 60s along the Iowa border
where cloud cover and the better chance of precipitation holds.
Elsewhere, 70s will be the rule. A fairly stout dry
northeast/easterly flow will drop humidity levels into the 20s
this afternoon across central Minnesota, and into west central
Wisconsin. Wind speeds will slowly decrease, limiting any fire
weather hazards.

.LONG TERM...(Monday through Saturday)
Issued at 255 AM CDT Sun May 20 2018

As discussed previously, the weak circulations associated with the
elongated trough over the plains, will slowly lift off to the
northeast. An upper ridge will commence Monday/Tuesday leading to
sunny skies and warmer temperatures.

By Tuesday night, the upper ridge will be west of Minnesota, with
an increasing low level jet across the Dakotas, and into western
Minnesota. Moisture will begin to pool northward with an area of
showers and thunderstorms developing along the nose of this jet
Tuesday night/Wednesday morning. Models continue to support the
best chance of widespread precipitation associated with the
nocturnal thunderstorm complex developing over eastern South
Dakota, southwest/south central Minnesota toward Wednesday
morning. Based on the upper level winds, this complex will likely
move to the southeast along the moisture gradient. As with any
thunderstorm complex that develops with the low level jet, most
will decay as the low level jet weakens in the morning. Wednesday
afternoon looks interesting in terms of redevelopment as outflow
boundaries associated with this complex will likely re-fire.
Where the storms re-fire remains questionable, but based on model
QPF, eastern Minnesota will likely be the target of
afternoon/evening thunderstorms. Based on the amount of
instability as widespread dew points rise into the 60s across
Minnesota, SBCAPEs could exceed 2000 J/KG Wednesday afternoon. I
wouldn`t be surprised to see a few strong or severe storms, but
wind shear looks weak, so organized severe weather doesn`t look

The warm and humid air mass will remain in place Thursday/Friday
leading to additional showers and thunderstorms. However,
placement, and how widespread these showers and thunderstorms
become is questionable. By late in the week, models appear to
support a cold front moving across the Northern Plains, and Upper
Midwest. This will likely produce a good chance of precipitation
along this front based on the amount of moisture and air mass in
place before the front moves through. Precipitable water values
remain well above normal for the second half of the week. Both the
EC/GFS, and their ensembles support precipitable water values
between 2-3 standard deviations above normal. This means that any
storms that develop will be very productive/efficient in terms of
heavy rainfall amounts/rates.

Once the cold front moves through the region, much drier air will
follow for the upcoming holiday weekend, with near normal


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 123 PM CDT Sun May 20 2018

MVFR cigs will continue to sag south this afternoon as dry
northeast winds push them down toward Iowa. Tonight, as surface
ridge shifts east, these clouds will start building back northwest
toward eastern SD. MKT/RWF look to get back into these clouds late
tonight, but SREF probs for MVFR or lower cigs show probabilities
quickly decreasing during the day Monday as these clouds try to
spread northeast during the day, so have maintained VFR cigs
everywhere else. There will also be a couple of sources of rain to
watch. One is a wave down by Omaha which will be lifting north
overnight, lifting rain into western MN, so brought a -RA mention
to RWF, with a vcsh to AXN. Second wave is the one currently over
central Neb and will come across southern MN Monday afternoon,
this may spread rain into the Twin Cities, but models are pretty
sparse with precipitation.

KMSP...Kept cigs VFR, but MVFR cigs will be possible Monday
afternoon, though heights will remain above 2k feet. There will be
two chances for some -RA, the morning with the Omaha wave and
afternoon with the central Nebraska wave. The Omaha waves look to
pass west of MSP, while forcing in the afternoon looks pretty
weak, with the NAM and GFS both dry for MSP, though we`ll likely
see a few drops in the afternoon.

TUE...MVFR cigs early, then VFR. Wind SE 5 kts.
WED...VFR with chc SHRA/TSRA late. Wind SE 5-10 kts.
THU...VFR. Chc -tsra. Wind S 5-10 kts.




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