Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 181045
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
645 AM EDT Tue Apr 18 2017

.NEAR TERM...(Today through Tonight)
Issued at 341 AM EDT Tue Apr 18 2017

...Increasing clouds with small chances of rain showers tonight...

High Impact Weather Potential...None.

Pattern Synopsis/Forecast...Strong surface ridge axis remains over
Michigan early this morning...producing mainly clear skies...cold
temps and a light/dry low level northeasterly flow across our CWA. A
look upstream shows low pressure developing to the lee of the
Rockies currently centered over South Dakota. Leading edge of
increasing mid/high clouds from this system has already moved into
the Western Great Lakes region...and will make steady eastward
progress into our CWA today as the upstream surface low reaches the
Arrowhead of Minnesota by late this afternoon. The low will then
continue NE thru Lake Superior this evening reaching the
Ontario/Quebec border by 12Z Wednesday...gradually filling as it
does so.

Latest short term models all agree that the majority of moisture and
lift associated with this system will slide north of our CWA. Precip
chances across our area will be limited to a relatively narrow area
of moisture and weak lift along and just ahead of the associated
cold front. Little to no instability will be available for the
development of thunder by the time the front and associated moisture
reaches our CWA later tonight. Expect increasing/thickening/lowering
clouds from NW to SE across our CWA today. Appears any chances of
precip will hold off until early evening and should be initially
limited to our far NW CWA along the southern periphery of the
moisture shield around the low center. Slightly better chances of
rain showers will develop late tonight after 06Z...and especially
after 09Z for the SE half of our CWA...as a second surge of moisture
rides northward along the cold front and into Lower Michigan.

Temps will be a bit warmer today...especially across NW Lower
Michigan...with high temps ranging from the upper 40s in Eastern
Upper Michigan to the mid 60s in our SW CWA. Low temps tonight will
range from around 40 in Eastern Upper Michigan to around 50 near
Saginaw Bay.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 341 AM EDT Tue Apr 18 2017

...More wet weather and potential flooding concerns...

High Impact Weather Potential: More rainfall with already saturated
conditions will increase the threat for flooding Thursday and beyond.

Pattern Forecast: Broad southwesterly flow aloft will stretch from
the western U.S....the southern branch of a split pattern across the
Pacific with a pair of upper lows east of the dateline.  A piece of
energy getting kicked out of the lead upper low currently near 145W
will arrive over the Plains later Wednesday...and strengthen as it
eventually crosses the Great Lakes in the Thursday/Friday time
frame.

A cold front associated with low pressure that will be moving to the
northeast away from the upper Lakes will cross the forecast area
Wednesday morning...with the trailing end of this boundary extending
back into NE/KS and serving as the focal point for lee cyclogenesis.
This low is expected to track along this frontal boundary northeast
and eventually across Lower Michigan during the day Thursday (a bit
of a northward shift in the track in recent runs).

Primary Forecast Concerns: Given already favorable hydrologic
conditions with very wet soils (top 1m soil moisture in the 95th
percentile across much of the forecast area) and streams already
running high...the focus will be on additional rainfall/runoff
heading into Wednesday night/Thursday as aforementioned surface low
heads in the direction of the Lower Peninsula. There is already a
broad pre-existing area of deep layer moisture extending from the
southern Plains east across the lower Mississippi Valley and into
the southeastern states ready to be drawn northward and across the
warm frontal zone ahead of the approaching surface low (precipitable
water values above 1 inch likely across much of WI/Lower MI.
Precipitation evolution is the main question with regard to QPF
potential...as can envision a convective complex/MCS forming east of
the surface low Wednesday evening along a low level jet axis
focusing across the mid Mississippi Valley...with the heavier cells
likely propagating east across southern portions of WI/Lower MI
while more "stratiform" area of rain spreads into northern Lower
Wednesday evening.  Have made a slight southward adjustment to
heavier precipitation axis for Wednesday night...focusing more on
northwest Lower (and can see the possibility that this axis may be
shifted farther south in later forecasts).

Another issue Wednesday night may be precipitation type across
eastern Upper...with a lot of room for evaporative cooling which is
leading to forecast thermal profiles with not a lot of room to
support all liquid precipitation.  Current consensus forecast
keeping things mostly rain across eastern Upper with some snow
possible Thursday morning across northern Chippewa county.  But this
is very much subject to change.

Precipitation expected to be ongoing Thursday morning...with a
couple of potential evolutions: 1) Rain moves through in the morning
followed by deformation precipitation band which could push into the
area during the afternoon or wait until evening 2) After initial
rain moves out in the morning more showery development occurs ahead
of main short wave trough...then followed by deformation zone
Thursday night.  Still plenty of time to sort that out but from a
forecast standpoint will continue with high precipitation
probabilities into Thursday evening.  Deformation zone will also
have a higher likelihood of seeing precipitation change over to all
snow Thursday night.

As for potential QPF and hydro concerns go...certainly a possibility
for another round of 1+ inch precipitation amounts across northern
Lower though still some variability in play.  Contingency QPF river
forecasts suggest issues on both the Manistee and Rifle Rivers in
northern Lower should these rainfall amounts come to pass.

.LONG TERM...(Thursday night through Monday)
Issued at 341 AM EDT Tue Apr 18 2017

Forecast trends are drier heading into the weekend...with little in
the way of QPF signals in the forecast guidance into the early part
of next week.  Temperatures will remain a bit cool Friday but a slow
warming trend with more seasonable temperatures expected for the
weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 645 AM EDT Tue Apr 18 2017

Low pressure will track NE out of the Northern Plains...thru Lake
Superior and into SE Ontario today and tonight. This system will
produce small chances of rain showers for Northern Lower Michigan
over the next 24 hours...with most of the associated precip
sliding north of our area. Aside from some lingering low stratus
early this morning within the interior areas of Northern Lower
Michigan...overall conditions will be VFR at all TAF sites today
thru most of tonight despite increasing/thickening/lowering
clouds. LLWS will develop tonight...and surface winds will steadily
veer along the southern periphery of this system.

&&

.MARINE...
Issued at 341 AM EDT Tue Apr 18 2017

Small craft advisories already in place in anticipation of
increasing winds today ahead of a surface low that will track
northeast out of the Dakotas and across Lake Superior tonight.
Easterly winds will veer more southeast and south this morning and
increase.  A passing cold front Wednesday morning will swing winds
around to the northwest for a time...then the approach of another
low pressure center forecast to track across lower MI on Thursday
will bring winds around to the east and should bring another round
of at least Small Craft Advisory conditions Wednesday night into
Thursday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 2 AM EDT Wednesday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 2 AM EDT Wednesday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 2 AM EDT Wednesday for LSZ321-322.
&&

$$

NEAR TERM...MLR
SHORT TERM...JPB
LONG TERM...JPB
AVIATION...MLR
MARINE...JPB



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