Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 180225
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1025 PM EDT Sat Jun 17 2017

.UPDATE...
Issued at 1025 PM EDT Sat Jun 17 2017

Low pressure continues to gradually deepen over Wisconsin and
Western Upper Michigan late this evening. Strong/svr convection
continues to fire along the associated cold front which extends
southward into Northern Illinois the southwestward thru Northern
Missouri and Kansas. Additional weaker convection is developing
around and along the northern periphery of the low itself from
Minnesota thru Northern Wisconsin and Upper Michigan into Northern
Lower Michigan. This northern area of weaker convection will
expand eastward into our CWA overnight...resulting in increasing
POPs across our entire area. Have made some minor modifications to
POPs for the overnight hours...but overall flavor of the forecast
remains unchanged. SPC has dropped the marginal chance of SVR
TSRA south of our CWA...with our entire area now in general
thunder for the remainder of the night. This seems reasonable
given significantly better instability and theta E ridging are now
south of us.

&&

.NEAR TERM...(Tonight through Sunday)
Issued at 333 PM EDT Sat Jun 17 2017

...Additional showers and storms through Sunday...

High Impact Weather Potential...thunderstorm chances through early
Sunday. Marginal risk for severe storms south of M-55.

Pattern Synopsis/Forecast...Fairly zonal strong belt of westerlies
is in place across the northern tier of states into the Great
Lakes around a closed upper low over south-central Canada...with a
warm and seasonably moist airmass across the Great Lakes into the
Ohio Valley. Upstream...strong short wave of Pacific origins is
moving through the northern high plains and expected to dip through
the upper Midwest and into the western Great Lakes tonight...carving
out deeper troughing across the Great Lakes Sunday through the
first half of the week with temperatures dipping back below
normal.

Primary Forecast Concerns...precip chances and timing. Thunderstorm
threat later this afternoon and tonight.

As anticipated...morning cloud cover thinned considerably across
most of the CWA...replaced by sct-bkn CU bubbling up across the
region...and a few showers trying to pop across eastern upper and
northern lower Michigan. Better shower/thunderstorm coverage
underway across central lower Michigan up into the Saginaw Bay
region...from a well defined MVC that has tracked from northern
Illinois into south-central lower Michigan this afternoon. All this
activity will carry into the evening hours before fading with
departure of MCV and loss of heating.

Stronger forcing arrives later tonight into Sunday as aforementioned
upstream short wave energy dips into the western Great Lakes...bringing
a deepening surface low and cold front through northern Michigan
on Sunday. Synoptic forcing and whatever instability remains out
there should result in a another round of widespread showers and
some thunder swinging through the region overnight through Sunday
morning...before a well defined dry slot punches into the region
and more or less diminishes shower chances by afternoon.

Severe storm chances...some modest instability and effect bulk
shear out there this afternoon (~500 J/KG and 35-45 knots
respectively per SPC mesoanalysis page) could lead to storm
organization and low end severe weather threat through early to
mid evening.

&&

.SHORT TERM...(Sunday night through Tuesday)
Issued at 333 PM EDT Sat Jun 17 2017

...Thunderstorms possible Monday and Tuesday afternoon...

High Impact Weather Potential...none.

Pattern Synopsis/Forecast...500 mb low moves into N Ontario out of E
Lake Superior during the day and pulls the rain out of the region as
as the 700-500 mb RH falls with the dry slot and the loss of daytime
heating during Sunday evening. By Monday morning, the next shortwave
trough is on the verge on moving across Lake Michigan. The models
show showers breaking out as the daytime heating continues. Model
show MLCAPEs a few hundred j/kg so will put thunder in for the
afternoon. As we lose the heating, showers and thunder threat abates
a bit. However, with more spokes of energy in the moisture and the
daytime heating will expect the showers to expand and there will be
a chance for thunderstorms in the afternoon.

Primary Forecast Concerns...Thunderstorm chances are somewhat low,
with the 500 mb shortwave moving through, but the cloud cover
probably being 70-80% coverage. If there can be any openings to
provide extra heating, then there could be a better chance, but at
this point, upper lows slowly moving through the Upper Great Lakes,
do not bode well for reduced cloud cover. More than likely there is
a good chance that the models are overdoing the thunder threat north
of M-55 as the self-destruct sunshine continues.

.LONG TERM...(Tuesday night through Saturday)
Issued at 333 PM EDT Sat Jun 17 2017

The beginning of our period starts with an upper level ridge over
the western states with broad troughing over the eastern half of the
US.  However...this will quickly transition to zonal flow by
Thursday.  By Friday, a closed low develops to the North of the
great lakes and skirts south of Hudson Bay...though the models
differ on the strength and progression of this feature.

All of that is to say that the zonal flow will allow for a few
pieces of energy to rapidly move across the lakes during the
period...and as is typical of this scenario, the timing of such
passages can be a challenge.  As the Canadian low develops, it will
try spin a front through the northern lakes for the Friday/Friday
night timeframe...providing the focal point for another chance at
rainfall, if it can make it this far south at all.

So in a nutshell: while there will be periodic chances of rainfall
through the extended, I think there will be longer stretches of
rain free conditions.  If I was going to bet on what day would be the
most likely for appreciable rainfall right now (and possibly some
thunder) it would Thursday. Daytime temperatures will be just a hair
below where they should be...with highs in the mid 70`s and
overnight lows in the 50`s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 727 PM EDT Sat Jun 17 2017

Low pressure will lift thru Northern Michigan over the next 24
hours...producing waves of showers and a few thunderstorms.
conditions will deteriorate to MVFR overnight into Sunday morning
as low level moisture increases ahead of the low center.
Conditions will improve to VFR Sunday afternoon...although the
chance of showers will remain in the forecast into Sunday evening.
Light/variable winds tonight into Sunday morning will become SW
and increase to 10 to 20 kts with higher gusts expected during the
afternoon.

&&

.MARINE...
Issued at 333 PM EDT Sat Jun 17 2017

Some gustiness out there this afternoon will linger into this
evening...although winds/waves will remain below small craft
advisory criteria. Some strong SW winds develop Sunday as low
pressure tracks through the region...and may require SCA`s for a
few marine areas on Lake Huron. But winds diminish quickly again
Sunday night into Monday.

&&

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

$$

UPDATE...MLR
NEAR TERM...TBA
SHORT TERM...TBA/JSL
LONG TERM...KAB
AVIATION...MLR
MARINE...TBA



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