Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 241735
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
135 PM EDT Sat Jun 24 2017

.UPDATE...
Issued at 1056 AM EDT Sat Jun 24 2017

Broad upper troughing engulfing the Great Lakes this morning, with
latest satellite showing one shortwave pressing across Wisconsin
and into Lake Michigan, while another larger shortwave is seen
working into Minnesota. The former wave is working on an axis of
higher low level theta-e air that is now aligned from lower
Michigan, back through Wisconsin. This seen clearly by increasing
and thickening cloud from the GTV Bay region back through
Wisconsin/western Lake Superior where there was some light shower
activity.

Early morning discussion hinting of possible light shower activity
across the GTV Bay region this morning is still a great idea (per
sprinkles reported at earlier at MBL. This shower chance will
increase eastward through the afternoon, and into NE lower as the
shortwave troughing and theta-e axis arrive, while shower
development being aided by diurnal instability generated under
steeper lapse rates/cooler air aloft. Cool temperatures and
relatively low sfc td`s only leading to up to 500-600j/kg of
MLCAPE. Did lower chances for thunderstorms, but there will at
least be some isolated activity. No severe storms.

The upstream stronger shortwave still expected to sweep across the
region tonight with decent overall deep ayer -divQ for continuing
shower chances, despite loss of daytime heating.

&&

.NEAR TERM...(Today through Tonight)
Issued at 404 AM EDT Sat Jun 24 2017

...Sunny early but more clouds/showers as day progresses...

High Impact Weather Potential: Minimal outside of ongoing hydrologic
issues.

Pattern Synopsis/Forecast: 03z surface/composite analysis shows
Michigan sandwiched between a pair of fronts...a northeast-southwest
oriented cold front stretched from the lower Great Lakes into the
Tennessee Valley...a second front was draped across northern Ontario
to the north of Lake Superior.  Much drier air has spread across the
area in the wake of the downstream cold front...with dew points
Friday afternoon falling into the upper 30s/40s inland from the
Great Lakes.  Water vapor imagery shows plenty of mid level
"weakness" spinning around the vicinity of the upper Great Lakes.
One short wave trough was moving through Lower Michigan into Lake
Huron...with a pair of vorticity centers over Minnesota... another
north of Lake Superior...and a larger upper low digging into North
Dakota.  Post-cold frontal drying evident in 00z APX sounding with a
deep (nearly up to 700mb) mixed layer...but colder mid level
temperatures upstream allowing from some skinny instability in
INL/YPL soundings along a low level theta-e ridge axis that
stretches from northern Illinois back to the northwest into the
northwest Ontario/southern Manitoba.

Upper low dropping into North Dakota is expected to spin across the
upper Midwest today...which will also push aforementioned vorticity
center over northern Minnesota east as well.  Upper low will make
its way into Lower Michigan tonight...while boundary to the north of
Lake Superior sags across the lake and possibly into the Upper
Peninsula.

Primary Forecast Concerns: Mainly cloud and shower chances today
with cooling mid level temperatures and approaching short wave
trough and upper low.  The former feature is already pushing another
mid cloud deck (and a few spotty radar returns) across Wisconsin/
western Upper Michigan and will spread into western Lower Michigan
later this morning.  Could be a few spits of rain with this initial
cloud cover later this morning into northwest Lower...but does
appear there will be an additional diurnal component to cloud cover
today...especially across northern Lower...where some skinny
instability will help generate some showers during the afternoon.  A
little less certain across eastern Upper with regard to
instability...though Lake Michigan/Huron breeze may serve as a focus
for showers probably only across Mackinac county.  Should also be a
risk for thunder especially south of M-32 this afternoon...with
diurnal shower coverage decreasing this evening.  But with the
approaching upper low...fairly deep layer deformation axis expected
to set up across Upper Michigan which is expected to focus a
continued threat for showers into tonight.  Will probably also see
some additional showers with the arrival of the primary mid level
circulation and associated dynamics.

From a hydrologic standpoint...rivers in the Rifle and Tobacco River
basins still running high due to recent rainfall.  Rifle River near
Sterling has leveled off and is running below the current forecast
so will have to evaluate ongoing warning.  Tobacco River at
Beaverton also appears to be cresting just below flood stage
(upstream gauge on the South Branch Tobacco River near Beaverton
also leveling off less than a foot below record stage).  Additional
rainfall today/tonight may slow the recession but outside of a slow
moving cell falling over the right part of a basin...not expecting
additional rainfall to cause a big rise in river levels.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 404 AM EDT Sat Jun 24 2017

...Continued cool with showers and perhaps a few storms...

High Impact Weather Potential...A few non-severe thunderstorms
possible Sunday and Monday afternoons.

Pattern Synopsis/Forecast...Sunday into Monday, Michigan will be in
line for a one-two punch of potent shortwaves/vort maxes rotating
around a broad longwave trough entrenched over the Great Lakes. The
first will exit the Thumb by Sunday afternoon while the second takes
a more southerly dive towards Lake Erie on Monday. Closer to the
surface, a weak cold front will drop south from Ontario on Sunday,
followed by a weak low with somewhat of a short-lived frontal
boundary that move across northern Lower Sunday night into Monday.
These features will generate showers and possibly some afternoon
thunderstorms both Sunday and Monday.

The parent longwave trough will be quite deep with 500 mb heights
falling to around 558 dam over northern Michigan on Monday...about 2
to 3 standard deviations below the mean for late June. Temperatures
aloft from 925 to 700 mb will also be around 2 to 3 standard
deviations below. So, expect a progressive cool down to continue
through the start of the work week as persistent NW flow advects
cooler air into the region. Highs will be in the mid to upper 60s on
Sunday and generally a couple degrees colder on Monday. Sunday
night`s lows will drop into the mid/upper 40s inland to around 50
near the shores.

Primary Forecast Concerns...Rain and thunder chances will be the
main forecast challenge. Lapse rates above 600 mb are looking a
little weaker for Sunday and Monday, and PWATs will be around 0.8"
or a little less. Given general NW flow pattern, expect the better
diurnal instability will be over northeast Lower, though we`re only
talking several hundred J/kg of MLCAPE at most. So, while
ingredients will be sufficient for scattered to perhaps numerous
showers (particularly during the daytime hours), expect any
thunderstorms that may develop to be pretty isolated, weak, and
short-lived...especially given the absence of deep layer shear.
Northern Lower will see the best forcing and hence higher PoPs than
eastern Upper.

.LONG TERM...(Monday night through Friday)
Issued at 404 AM EDT Sat Jun 24 2017

High impact weather potential...Thunderstorms possible at times
Wednesday afternoon through Friday.

Upper trough and unseasonably cool airmass finally eject to the east
Monday night with heights rising through midweek as upstream ridge
makes quick progress towards the Great Lakes. Increasing subsidence
from this ridge and a surface high will lead to a period of dry
weather that will likely continue through Wednesday morning. The
remainder of the forecast period looks rather active and wet as
models track several developing lows from the Central/Northern
Plains into the Great Lakes, interacting with a potentially very
moist airmass. Being this far out, plenty of questions to still be
answered, but periods of showers and storms are looking increasingly
likely for northern Michigan through the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 128 PM EDT Sat Jun 24 2017

Troughing and cool air aloft with disturbances passing through
over the TAF period will result in scattered showers and isolated
thunderstorms. These will mainly be tied to afternoon diurnal
heating. Deeper lower level moisture rolls in here later this
afternoon and mainly tonight, and MVFR CIGS are becoming more
likely to develop. Winds rather light through the period with a
tendency to go onshore in the afternoons.


&&

.MARINE...
Issued at 404 AM EDT Sat Jun 24 2017

Winds not expected to be significant this weekend as gradient
will be relatively weak. Lake breezes likely to pop along
northeast Lower and southeast Upper shoreline this afternoon. A
little more persistent west/northwest wind expected for Sunday.


&&

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

$$

UPDATE...SMD
NEAR TERM...JPB
SHORT TERM...MEK
LONG TERM...MEK
AVIATION...SMD
MARINE...JPB


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