Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 190906
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
306 AM CST Sun Feb 19 2017

.SHORT TERM...(Today and tonight)
Issued at 306 AM CST Sun Feb 19 2017

Concerns in the short term include dense fog early this morning,
record highs this afternoon and finally thunderstorm chances late
tonight.

Dense fog started to develop shortly after midnight across far
southern MN near KAEL and across portions of central MN. However,
since then some improvement has occurred, which seems tied to an
increase in high level cloudiness from the west. We are certainly
not out of the woods yet as widespread dense fog covers northern
IA and parts of SE MN. The CAMS are split on whether or not the
dense fog to our south advects north this morning. Our MPXWRF and
the NMM/ARW basically keep it in place while both HRRR solutions
bring it north, staying just west of the Twin Cities. For now,
have opted hold off on a dense fog advisory and use areas of fog
in the forecast, mainly because of thicker and more widespread
high level clouds spreading across the MN CWA.

For the day ahead, it will be another record setter for central
and southern MN. A combination of mix-down from 925 mb along with
bias corrected guidance yielded highs in the lower to middle 60s
from the Twin Cities on west and south with 50s to the north and
east. Records for today include 56/1981 at KSTC, 57/1981 at KMSP
with 60/1930 at KEAU. Forecast values are 59, 61 and 56 degrees
respectively.

Tonight will begin dry, but a Pacific cool front will reach the
eastern Dakotas late in the night. Moisture will be increasing
ahead of the front along with elevated instability. Mid level
lapse rates are progged to be greater than 7 deg C/KM. The CAMS
are in good agreement that only a few showers and isolated
thunderstorms are possible from west central through south central
MN in the 09z-12z time frame. The shower/thunderstorm activity
then really expands from southwest to northeast after 12z, which
is the beginning of the long term.

With the increasing moisture and low level winds tonight, low
temperatures are going to be way above normal by leaps and bounds.
Current projections are for lows around 50 in the MN River Valley
with middle 40s in the Twin Cities. Lows to the north and east of
KMSP will be in the upper 30s to lower 40s. We will set a record
high minimum temperature in the Twin Cities for Feb 20th which is
currently 35 degrees set in 1899. We could also tie or break the
all time record high minimum for the month of Feb (44 degs 1930)
if we don`t fall below 44 by midnight Monday night. Currently we
have 45 degrees forecast.

.LONG TERM...(Monday through Saturday)
Issued at 306 AM CST Sun Feb 19 2017

Confidence remains high for the abnormally mild temperatures to
continue through Wednesday as the upper air pattern holds with an
elongated upper ridge centered across Canada, through the Great
Lakes. Slowly this pattern will change by the ladder part of the
week as a mean trough across the western Pacific moves inland, and
becomes established across the western 2/3s of the United States
next weekend.

First, Monday`s weather pattern is more conducive for mid April as
precipitable water values rise above one inch. The latest NAEFS has
PWATs/85H-92H Specific Humidity levels nearly 5 standard deviations
above normal. Standard deviations above 3 are impressive, but when
these values approach or exceed 4 or 5, then you are looking at
extreme/historical conditions. Over the past few days the forecast
has been explaining the anomalous mild temperatures, but other
aspects of weather can be included in this discussion, which is the
high water content in the atmosphere. Not only are the chances of
thunderstorms likely on Monday, but the potential of heavy rainfall
is becoming possible. Current QPF amounts seem low considering the
amount of forcing and PWATs Monday. I wouldn`t be surprised to see
rainfall rates of one half inch per hour or greater if convection is
stronger Monday afternoon along the cold front. Once this front
moves by, the air mass doesn`t change much which leads to the
continued mild/unseasonably temperatures.

The potential of a very strong winter storm is still on track to
affect a large portion of the Plains, and into the Upper Midwest,
western Great Lakes late next week. Although the GFS has shifted
southward with the latest forecast run (00Z/19), both the EC/GEM
remain favorable for southern Minnesota to receive several inches of
snow Friday. One of the aspects of this storm is the lower chances
of a period of rain before the precipitation changes over to snow.
This is related to a colder air mass having more affect across the
Northern Plains, Upper Midwest behind a weak system Wednesday. This
system will also have an impact on how much drier air becomes
entrained which may lower snowfall totals, or shift the storm system
further to the south as the current GFS indicates. Therefore, for
those looking for an absolute snowstorm, please check later forecast
and see how this system evolves. It is also not wise to pinpoint
absolute snowfall amounts this far in advance where the current
storm that will eventually led to the snowstorm is 1000 miles off
the west coast early this morning. One aspect to this storm whether
we get snow or not, is the cooler temperatures next weekend, or at
least more normal for late February/early March.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1055 PM CST Sat Feb 18 2017

VFR conditions expected throughout this TAF package. Upper-level
ceilings will prevail through the next 24 hours, mostly BKN than
anything else, dropping from around 20 kft to around 10 kft.
Light and variable winds overnight will become southeasterly
tomorrow with speeds generally in the 5-10 knot range, though
western MN could have higher speeds and gusts. Towards tomorrow
evening, low level winds are likely to increase to the 40-50 knot
range from the south, potentially creating LLWS conditions across
the area. Short-term models are showing better agreement in this
thinking but with LLWS not expected to develop for another 20-24
hours, will hold of its inclusion to ensure following model runs
maintain consistency.

KMSP...No significant weather impacts expected through 00z
tomorrow evening. Beyond 00z, chances are increasing for LLWS
conditions developing as winds up to 2 kft increase to 18040G55kt.
Will need to see if this thinking is maintained in upcoming model
runs before going ahead and including it in the TAF.

/OUTLOOK FOR KMSP/
Mon...MVFR with SHRA Likely. ISOLD TSRA. Wind S at 10 kts.
Tue...VFR. Wind SW at 5-10 kts.
Wed...VFR. Wind SW at 10G15 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...RAH
LONG TERM...JLT
AVIATION...JPC



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