Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 271910

Area Forecast Discussion
National Weather Service Gaylord MI
310 PM EDT Tue Jun 27 2017

.NEAR TERM...(Tonight through Wednesday)
Issued at 310 PM EDT Tue Jun 27 2017

High impact weather potential: Heavy rains moving in Wednesday

Pattern synopsis and forecast:

Upper level troughing was pushing across the eastern Great Lakes
this afternoon, while ridging was gradually moving across the nrn
plains. Nrn Michigan was in between in the NW flow aloft with a weak
shortwave sliding SE through the western Great Lakes. There was some
increase in higher level cloud with the wave, while diurnal cu has
also blossomed across areas away from the stabilizing westerly flow
coming off Lakes Superior and Michigan. We still had some rather
steep lapse rates aloft, near 7c/km, with lake breezes developed
across interior eastern upper. The lake breeze is trying to get
going across Lake Huron, but the overall slightly stronger gradient
flow in nrn lower has slowed this process. Further upstream, a more
defined shortwave trough was seen pushing across Montana. The
associated sfc low was NE of there in Canada, with a trailing warm
front stretched southward, working it`s way toward the central
plains. Shower development out ahead of the warm front has just been
spotty, as deeper moisture has yet to be advected into the central
and nrn plains.

Heading through the afternoon, lake breezes are still expected to
develop across NE lower and both there and eastern upper (mainly
Mackinac county) may see a few showers. Still doubt any thunder in
NE lower, but can`t say there isn`t a "slight" chance. Instability
still not expected to be much, around 200-300 MLCAPE/700-900 SBCAPE.
These showers fade by sundown with the departure of the weak
shortwave. Skies will be mostly clear through the night, with maybe
some increase in higher level clouds overnight as the aforementioned
Montana shortwave ejects into the upper Mississippi valley. Lows
tonight in the upper 40s to lower 50s most areas, with low lying
areas down into the middle 40s. Could be cooler, but an increase in
winds just off the sfc not allowing that.

The main weather rolls in Wednesday. The shortwave pushes into the
western Great Lakes by the afternoon, the system warm front into nrn
Michigan by evening. Forcing is looking pretty darn good with low to
mid level waa strong, highlighted by a 50-55kt LLJ, resulting in the
strongest theta-e convergence across primarily eastern upper/far
NW/nrn lower Michigan. There will also be a nice pocket of upper
divergence in a double jet structure aloft. Throw in some additional
DPVA forcing and see no reason to sway from the beginnings of
potential heavy rains developing by late afternoon and into the
evening (more on that below). Not much, if any, instability
foreseen. Again, after modifying soundings, see only a couple
hundred j/kg possible with a strong 800-700mb warm nose/cap. Removed
all thunder from the Wednesday forecast. Skies to become cloudy by
afternoon, with temperatures still being able to climb into a good
chunk of the day. Highs in the middle 70s most areas.


.SHORT TERM...(Wednesday night through Friday)
Issued at 256 PM EDT Tue Jun 27 2017

...Heavy rain event possible Wednesday night...

High impact weather potential...Heavy rainfall/flooding possible
Wednesday night.

Pattern synopsis/forecast...Sfc low tracking out of the Plains will
cross the region late Wednesday/early Thursday. Cold front passes
through Thursday. Secondary low develops on the cold front to our SW
and tracks N Friday into the Great Lakes region.

Primary forecast concerns/challenges...Potential heavy rain event
setting up Wednesday night into early Thursday.

Warm advection/isent lift and deep moisture ahead of the low will
move in on SW flow out of the Gulf Wednesday afternoon and evening.
LLJ of 50kt+ develops to our SW which lifts the
warmth/moisture/instability over the front with some help from the
right rear quad of 100kt+ upper jet. Column mean RH values are high
(80%+), warm cloud depths are 11kft deep and PWATs are 1.5"+ from
00z THU to 18z THU. Best forcing is ahead of the LLJ which should
happen early on in the event 00-06z. Model differences still in
timing of SW-NE oriented cold front moving through the region. CAPE
values on slower models peak around 1000 J/kg before the front moves
through Thursday. Any convection that develops ahead of the cold
front could be slow moving due to orientation of mean wind/LLJ.

With all of the rainfall over the past week, 6HR flash flood
guidance values are down to near 1.5" over parts of the CWA. Model
6hr QPF values of 1.00 to 1.25" so should be close. Fast movement of
initial wave lead me to believe that flooding is possible, but
widespread flash flooding threat not great enough to warrant watch.
Will issue statement on flooding possibility with event still 48+
hours away. WPC has placed all of our CWA in the marginal to slight
risk of excessive rainfall for day 3.

Next shot of rain arrives Friday as slug of moisture with second low
moves into the Great Lakes.


.LONG TERM...(Friday night through Tuesday)
Issued at 256 PM EDT Tue Jun 27 2017

Another long wave trough covers the western Great Lakes through
early next week with a nearly zonal flow likely developing toward
midweek. Upper level disturbances moving through the trough in
combination with instability from heating of the day will lead to
shower chances (and perhaps a little thunder) through Monday. High
pressure is then expected to lead to precipitation free conditions
Tuesday. Temperatures will be generally a few degrees below average
for late June/early July.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 126 PM EDT Tue Jun 27 2017

...VFR this TAF period...

High pressure crosses south of the srn Great Lakes through the TAF
period, making way for the approach of low pressure and a warm
front by Wednesday afternoon. Cumulus today will gradually
disperse into the evening with mostly clear skies anticipated for
tonight with maybe just some high level cirrus increasing late.
This higher level cloud will thicken through Wednesday with
showers developing Wednesday afternoon and spreading east through
the evening. The rainfall will start to get fairly heavy late in
the afternoon and especially in the evening, especially for PLN.
It will not be until then when CIGS/VSBYS are expected to go


Issued at 256 PM EDT Tue Jun 27 2017

Sfc high pressure crosses south of the Great Lakes through tonight,
with low pressure and a warm front working into the region Wednesday
afternoon and Wednesday night. The cold front then crosses through
the day Thursday. The pressure gradient really starts to tighten
Wednesday and Wednesday night for solid advisory level gusts. The
warm front and low pressure Wednesday afternoon and night will also
bring periods of showers and thunderstorms with pretty heavy
rainfall. Southerly winds will turn more westerly behind the cold
front Thursday and Thursday night.


LH...SMALL CRAFT ADVISORY from 8 PM Wednesday to 8 AM EDT Thursday
     for LHZ346-347.
     SMALL CRAFT ADVISORY from 8 AM Wednesday to 8 AM EDT Thursday
     for LHZ348-349.
LM...SMALL CRAFT ADVISORY from 8 AM Wednesday to 8 AM EDT Thursday
     for LMZ323-341-342-344>346.
LS...SMALL CRAFT ADVISORY from 8 PM Wednesday to 8 AM EDT Thursday
     for LSZ322.
     SMALL CRAFT ADVISORY from 8 AM Wednesday to 8 AM EDT Thursday
     for LSZ321.


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