Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 250346
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1146 PM EDT Mon Apr 24 2017

.UPDATE...
Issued at 939 PM EDT Mon Apr 24 2017

Plenty of cirrus out there this evening, though said cloud cover
is rather thin. Thickening trend still expected tonight as warm
advection increases here and upstream. 00Z APX sounding indicates
massive amounts of dry air between 825mb and 450mb, with dew point
depressions around 40C. Upstream precip/virga in and near western
WI will continue to evaporate as it tries to move east.

Winds have managed to go light in some coastal areas, where a
cool/stable marine airmass is resisting mixing despite the
rather tight pressure gradient. This will require a slight
downward adjustment to temps in a few spots, including the Straits
and MBL/FKS/Leland.

&&

.NEAR TERM...(Tonight through Tuesday)
Issued at 339 PM EDT Mon Apr 24 2017

High impact weather potential: None.

Pattern synopsis and forecast:

High pressure extends from Ontario into Quebec this afternoon, with
low pressure in the central and north central conus. A warm front
extended from this low pressure into MN/srn WI and srn Lake
Michigan. One shortwave was lifting through the Dakotas underneath
decent double jet upper divergence and strong low to mid level warm
advection. The result was an area of showers within deeper moisture,
moving up toward south central Canada. Across nrn Michigan, a band
of clouds in higher level warm advection has lifted north of
Chippewa county, while only cirrus was approaching from the west.
Thus, it was mainly sunny, and with a very dry air mass and warm
temperatures across much of NW lower, humidities have tanked there.
A gusty southeast wind was present most areas, which is also
providing a cooling effect off Lake Huron into eastern upper and NE
lower due to the still cold water.

More quiet weather heading into tonight and Tuesday, although we
will see some change. Upper troughing will slowly edge closer to the
western Great Lakes, with weak shortwaves bringing in added higher
level cloud. In addition, persistent gusty SE flow will draw in
added lower level clouds from closed system in the Carolinas. The
atmosphere will not be able to moisten up enough, nor will the
stronger advections and upper dynamics out west get close enough for
generating any precipitation in nrn Michigan. So, the only change
will mainly be focused around higher humidities and cloudier skies.

The cloudier skies may try and suppress high temperatures somewhat
tomorrow, but not just sure on that yet. Will ride the upper 60s in
downsloping areas of NW lower, to cooler low 50s to low 60s in
coastal areas of Lake Huron. Lows tonight much less chilly due to
increased winds just off the sfc. Readings in the low to mid 40s
will be common and slightly milder in downsloping regions of NW
lower.

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 339 PM EDT Mon Apr 24 2017

...Much more active midweek...

High impact weather potential: Chance of thunderstorms Wednesday
afternoon through Thursday, some of which may include heavier
downpours. Small, low confidence, threat for a severe storm or two
Wednesday afternoon-evening.

Pattern Forecast: By Tuesday night, troughing across the midsection
of the country is expected to sharpen as a shortwave (currently just
off the coast from the Pacific NW via this afternoon`s water vapor
imagery) races through the four corners region aiding in
cyclogenesis lee of the Rockies. Developing low pressure strengthens
as it progresses northeastward toward the Great Lakes during the
midweek timeframe with the wave eventually becoming negatively
tilted. Open tap to Gulf moisture will allow for increasing deep
layer moisture Tuesday, but more so Wednesday-Thursday with PWs
progged to climb to near 1.25 inches. Threat for showers arrives
Tuesday night into Wednesday across far NW Lower/eastern Upper
before spreading eastward Wednesday night into Thursday (along with
the threat for thunderstorms) as better forcing and mid-level
dynamics rotate through the region.

Primary Forecast Concerns: Main forecast concerns/challenges revolve
around the Wednesday through Thursday timeframe and include PoPs,
thunder chances, and any potential for severe weather and heavier
periods of rainfall.

Scattered shower chances begin to increase to an extent Tuesday
evening-night, mainly across far northwest Lower and eastern Upper,
however the bulk of precip is expected to remain well off to our
northwest and across the lower Mississippi Valley. By Wednesday
morning into the afternoon, strung out low pressure is expected to
move from the mid-Mississippi Valley into the Western Great Lakes
with a warm front draped across southern Lake Superior into Ontario
and a trailing cold front southwestward toward the southern plains.
All this to say, gradually increasing shower chances to a greater
extent Wednesday afternoon and especially late Wednesday night-
Thursday. Scattered thunder threat also increases during this
timeframe as a plume of several hundred J/kg of MLCAPE is progged to
work its way across sections of northern Lower (some guidance
suggests upwards of 1,500 J/kg MLCAPE...but this seems quite a bit
overdone considering the mid-60s dewpoints also progged). With the
potential for abundant mid-high clouds on Wednesday, realizing any
significant amount of instabilty remains low confidence. 0-6 km bulk
shear values Wednesday afternoon-evening surge to more than 50 kts
across the area, but overall severe threat is limited by the
aforementioned low confidence instability and lack of forcing
locally. Low-level winds likely even too strong to develop lake
breezes to be a focus for convective initiation.

24/12z suite of guidance doesn`t provide much in the way of
confidence as to how Wednesday night through Thursday will play out
due to fairly significant differences (even only 72 hours away) with
respect to the overall evolution/amplification of low pressure along
with cold front timing and axis of heaviest rainfall. As was
mentioned earlier, open tap to Gulf of Mexico moisture aids in
increasing moisture with Pwats over an inch across the region. When
combined with what`s expected to be a tight baroclinic zone along
the front and fairly strong mid-level dynamics/forcing, the
potential is there for periods of heavier rainfall. The question
is...where does that set up? Trends suggest it will be off to our
west across Wisconsin, perhaps clipping far western sections of the
area from time to time Wednesday night through Thursday. Worth
watching what should be an interesting evolution to this system over
the next couple of days.

Well-above normal high temps (10-15 degrees above the normal 53-58
degrees) Wednesday...ranging from the upper 50s across E. Upper to
the low-mid 70s south of the bridge (cooler near the lakes). Highs
fall back closer to normal Thursday.

.LONG TERM...(Thursday night through Monday)
Issued at 339 PM EDT Mon Apr 24 2017

Active weather will continue through the extended period as a series
of disturbances push through the area. There could be a brief break
in precip Friday as high pressure noses in. But aside from that, a
slow moving system lifting through the Great Lakes will make for a
rainy weekend, continuing into early next week. There will be cold
air filtering in as these systems exit, and areas especially in
eastern upper could see a few flakes mixing in with any precip, but
nothing of real significance.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1146 PM EDT Mon Apr 24 2017

VFR, becoming MVFR Tue evening. LLWS tonight.

High pressure will remain near Hudson Bay, while low pressure
evolves in the central/southern plains. Present ese low-level flow
will gradually veer se and then s during the forecast. This will
eventually bring increased moisture to the region, though this
process will be gradual. Clouds will thicken and lower tonight
and especially Tuesday, but cigs are expected to remain VFR thru
the day. Stratocu will likely lower to MVFR levels Tue evening,
initially at APN and lastly at MBL.

E to se winds will eventually become south on Tuesday, and will
be somewhat gusty again in the afternoon. LLWS tonight, with
stronger se to s winds just off the surface.

&&

.MARINE...
Issued at 339 PM EDT Mon Apr 24 2017

High pressure extending from Ontario to Quebec, combined with a warm
front lifting north into nrn Michigan tonight, will further tighten
up the pressure gradient. Current advisory level winds over most of
the nearshore waters will continue into Tuesday, before low pressure
and a cold front advance into the region Wednesday and waken the
gradient. Shower and thunderstorm chances increase Tuesday night
through Thursday, with at least the potential for strong
thunderstorms Wednesday afternoon and Wednesday evening. Winds will
remain south to southeast through the forecast period.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 5 PM EDT Tuesday for LHZ345>348.
LM...SMALL CRAFT ADVISORY until 5 PM EDT Tuesday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 5 PM EDT Tuesday for LSZ321-322.
&&

$$

UPDATE...JZ
NEAR TERM...SMD
SHORT TERM...MJG
LONG TERM...ALM
AVIATION...JZ
MARINE...SMD



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