Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 220229
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1029 PM EDT Wed Jun 21 2017

.UPDATE...
Issued at 1029 PM EDT Wed Jun 21 2017

A quiet evening in progress in the north woods, though some
changes are afoot. Earlier isolated showers that popped along the
eastern upper MI lake breeze collision have long since died.
Patchy leftover diurnal cu/stratocu lingers, primarily in n
central and ne lower MI. More extensive mid-cloud is just to our
nw, covering much of Superior. Some actual showers are seen over
western Superior and far western upper MI, with more vigorous
convection further west yet over central/northern MN.

Zone of strongest 850mb warm/moist advection will quickly migrate
eastward tonight, encroaching on the western lakes late tonight.
This will result in convection developing ahead of upstream
activity, and north of the warm front that now sites from ne Iowa
to central OH. This activity will start to poke into nw lower and
western Chip/Mack after 06z/2am, and especially after 5am. Have
slowed onset of precip a bit, but will still boost pops late in
the overnight in nw lower MI.

Richer moisture/instability may arrive just in time for an
organized MCS to push in from the w and wnw. This perhaps opens up
a marginal svr threat, probably not til after 1st light (which is
of course quite early). This is line with the last few SPC day 1
outlooks.

&&

.NEAR TERM...(Tonight through Thursday)
Issued at 303 PM EDT Wed Jun 21 2017

...Active weather from early Thursday morning through Thursday
night...

High impact weather potential...thunderstorms moving across the
region overnight.

Pattern synopsis/forecast...Upper air ridge axis moves east of MI by
morning. Sfc warm front across the plains lifts northeast this
afternoon and evening into WI/MI. Upper jet shifts from southern
Great Lakes to the northern lakes as well. Ageostrophic flow
enhances 50kt LLJ that sets up across WI into nrn MI. Moist unstable
air lifted over the frontal boundary will help cluster of
thunderstorms develop around the Arrowhead of MN/Nrn WI/W UP late
this evening. Thunderstorms should drop SE across Nrn Lower MI
toward best instability across Srn MI toward morning.

Then cold front currently over the northern plains approaches and
crosses our region Thursday night. Open Gulf and abundant moisture
already pushed north by TS Cindy should help thunderstorms with some
very heavy rain move into MI.

Primary forecast concerns/challenges...Severe and heavy rain potential
after 08z Thursday morning and again Thursday afternoon and
evening.

Model soundings show instability lacking overnight. In fact, no CAPE
forecast at KTVC and around 100 J/kg at KLDM 06-12z. Trend has been
for the most unstable air to be farther south across southern MI, but
thunderstorms develop in very unstable air across C WI and track
across lower MI. Shear profiles impressive and with 40kt winds
just off the surface, could see a few thunderstorms producing near
severe gusts. PWATs from 1 to 1.5" so while there may be heavy
rainfall, should not be significant. Most models center heaviest
rainfall across areas south of M-32 and based on FFG values, this
area most able to handle a bout of heavier rainfall.

However with more storms developing Thursday afternoon and evening
in high CAPE environment, will have to monitor for flooding
potential, especially in those areas that get rainfall late tonight.
Heavy rain a definite possibility Thursday afternoon and evening as
PWAT values approach 2", column mean RH values near 90% and
possibility of training echoes due to steering flow and LLJ
orientation. CAPE values impressive for up here around 2000 J/kg by
afternoon in areas from KTVC-KGLR-KAPN south with 0-6km Bulk Shear
40+kts, so severe threat also possible. WPC has outlooked the area
for slgt risk of excessive rainfall.

&&

.SHORT TERM...(Thursday night through Saturday)
Issued at 303 PM EDT Wed Jun 21 2017

...Active weather into Friday then showery and cooler for the
weekend...

High Impact Weather Potential...Thunderstorm chances and a marginal
risk for severe through Thursday night. Heavy rain also possible for
parts of the CWA.

Pattern Synopsis/Forecast...Long wave troughing encompasses much of
central and eastern Canada...and down into the Great Lakes region
while long wave ridging continues to build northward along the west
coast toward the Gulf of Alaska. This pattern will largely remain
intact over the next several days as ridging locks in along the west
coast and long wave troughing deepens through the Great Lakes. Most
active part of the forecast will occur Thursday into early Friday
with surface low pressure moving through the northern lakes region
and a slow moving boundary sliding across the Great Lakes. Cooler
weather arrives for the weekend along with the possibility for
daytime instability showers...augmented by the passage of one or
more short wave troughs.

Primary Forecast Concerns...First forecast concern revolves around
heavy rain threat Thursday into Friday as plume of very moist air
surges into the Great Lakes from the Gulf (PW values pushing 2
inches across lower Michigan) ahead of the incoming short wave
trough and cold front. Lead short wave kicks through the upper
Midwest and northern lakes region...late Thursday into Friday
driving a smaller secondary surface low and the front through the
region through Friday morning. Augmented by a buckling upper jet
core/lowering heights across the northern lakes...we still
anticipate another round of showers/storms to develop across the
upper Midwest later Thursday and slide through the region Thursday
night into Friday. Swath of heaviest QPF is still a bit uncertain
and will depend on (amongst other things) convective evolution
tonight into Thursday...placement of boundary and initiation of the
next round of convection heading into Thursday night. Most guidance
solutions have shifted the heaviest rainfall northward into northern
lower Michigan...hence the northward shift of the Day2 excessive
rainfall slight risk into our area. Will just have to see how things
evolve but the good news is that while we have been on the wetter
side in recent weeks...forecast rainfall amounts (mainly under 2
inches) are still expected to largely stay under flood guidance
values.

Second concern...marginal severe risk later Thursday through
Thursday night. Very strong mid level flow pushing 70 knots/
resulting 0-6 KM bulk shear develops across the northern lakes
Thursday night into Friday although displaced and on the northern
fringe from better instability axis that will be across central and
southern lower Michigan. SPC Day2 outlook with a marginal risk south
of M-72 keys off that better instability axis sitting off to our
south. But again...instability axis placement will depend on just
where the boundary ends up.

.LONG TERM...(Saturday night through Wednesday)
Issued at 303 PM EDT Wed Jun 21 2017

The overall theme for the extended will be "cooler and unsettled".
Broad troughing will develop in the upper levels on Sunday and stick
around through Tuesday.  This will keep cooler conditions over the
Great Lakes...with occasional short waves sliding down the trough to
bring periodic chances of precipitation and possibly some thunder.
The timing of these wet/dry times will be the forecast challenge
through the extended period.  Readings will begin to moderate toward
midweek...as troughing slides east.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 733 PM EDT Wed Jun 21 2017

Shra/tsra expected very late tonight/Thu morning.

High pressure is over Lake Erie and moving ese. Moist southerly
flow will increase behind the high. Showers/t-storms are expected
to develop upstream in MN/WI and move eastward tonight, impacting
parts of northern lower MI very late tonight and Thu morning.
Some TSRA are possible, accompanied by lowering cigs and (at
times) vsbys. Some MVFR cigs are expected at times Thursday.

Winds will become light tonight, with an increasing southerly
breeze Thursday (gusty in spots).


&&

.MARINE...
Issued at 303 PM EDT Wed Jun 21 2017

Light winds are expected overnight with increasing winds expected
Thursday. A small craft advisory may be needed from mid morning
Thursday through the afternoon. In addition, thunderstorms are
expected to move in in the early morning hours Thursday. The
chance for thunderstorms, some possibly severe, will then continue
through the day.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...JZ
NEAR TERM...KJF
SHORT TERM...TBA
LONG TERM...KAB
AVIATION...JZ
MARINE...KJF



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