Area Forecast Discussion
Issued by NWS Gaylord, MI

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539
FXUS63 KAPX 270140
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
940 PM EDT Mon Jun 26 2017

.UPDATE...
Issued at 940 PM EDT Mon Jun 26 2017

Precip band remains fairly substantial, currently stretching from
Drummond Isl to CAD. It is starting accelerating se-ward as low
pressure moves east from Georgian Bay. And the back edge is quite
sharp; the Sault is already cloud-free below 12k ft. We remain on
target in getting this precip out of here tonight, exiting the
OSC/Tawas area by 3-4 am. But, in the interim, have boosted
pops/QPF considerably.

&&

.NEAR TERM...(Tonight through Tuesday)
Issued at 239 PM EDT Mon Jun 26 2017

High impact weather potential: Isolated thunderstorms again. No
severe storms, but small hail possible.

Pattern synopsis and forecast:

Large scale upper troughing and cooler conditions continuing across
nrn Michigan. Sfc low pressure still in eastern upper with numerous
rain showers buried in the better low level cyclonic flow.
Meanwhile, there have been a few holes in the cloud cover along and
south of M-68 in nrn lower. Not much heating, but we have been able
to pop off some diurnally driven rain showers in a moist air mass
underneath the persistent steeper lapse rates aloft around 6.5c/km.
Further upstream, a upper level low was dropping SE and into Lake
Michigan. Moisture was increasing out ahead, with DPVA and diurnal
processes helping to fire off more rain showers. The main shower
activity however, remained on the W/NW flank of the upper low,
within the deformation zone and deepest moisture. Instability as
earlier thought, has been rather minimal. virtually none across
eastern upper, 100-200j/kg in most of nrn lower, to up to 500j/kg
the most closer to Saginaw Bay.

The sfc low pressure will slide east of eastern upper through the
later afternoon and evening, and the stronger low level convergence
will start to wane. This will help to break up the steadier nature
of the rainfall. The deformation rains however, will be wrapping at
the same time, and also down across NW lower. This upper low makes
it into SE lower Michigan by midnight with the help of another wave
seen diving through Ontario, and then both will be east of us
Tuesday. The deformation will be weakening with time as the upper
low gets further away through evening. With this being the main
forcing, am expecting incoming showers to be breaking up with time
as well. This trend has been picked up by higher resolution data,
and have gradually stepped down chances for rain with time (numerous
west/scattered east this evening...becoming isolated to ending
overnight.

This whole transition will slowly put nrn Michigan in NW flow aloft
on Tuesday, as ridging tries to work into the upper midwest. There
is some drying that takes place into Tuesday, but overall PWATS
remain around 0.75". Am expecting a decent cu field to develop late
morning to afternoon with a tendency for onshore flow to develop,
especially across interior eastern upper and far NE lower. The cu
field is likely to be most dense in these areas. There is not much
in the way of forcing/dynamics aloft with some weak vorticity
dropping into the region, but maybe a shower or two can develop
within the lake breeze convergence. No thunder chance seen at this
point.

Lows tonight in the lower 40s north to the upper 40s in far NE
lower. Highs Tuesday in the lower half of the 70s most areas,
possibly middle 70s in downsloping regions of NE lower.

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 239 PM EDT Mon Jun 26 2017

...Heavy rain event possible Wednesday night and Thursday...

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

Pattern synopsis/forecast...Surface low moving across Southern
Canada will drag frontal system east through thursday. as the system
runs into strong high over the SE US, front lags the low and becomes
more parallel to mean flow. In addition, strong 60kt+ LLJ develops
over the midwest Wednesday and moves into MI Thursday. Abundant
moisture available with Gulf wide open. Set up is similar to last
week`s heavy rain event, without the tropical system.

Primary forecast concerns/challenges...Potential heavy rain event
setting up Wednesday night into Thursday. Initially warm front
approaches region Wednesday evening. Deep moisture and strong
isentropic ascent as LLJ pushes Gulf air over the front. Lift
enhanced by left exit region of 100kt upper jet. Mean RH values
close to 90% with PWATs over 1.5" for a 12 hour span. Then SW-NE
oriented cold front crosses region Thursday. LLJ and mean flow
nearly parallel which could lead to slow movement of heavy rain
producing cells. However, CAPE values remain low throughout the
event which could mean heaviest rain falls south of CWA. As always,
the trick as with the last system, will be to narrow down where
heavy rain swath will occur.

With all of the rainfall over the past week, 6HR flash flood
guidance values are down to near 2" over southern and eastern parts
of the CWA. QPF values of over 2" are possible, WPC has placed all
of our CWA in the marginal to slight risk of excessive rainfall for
day 3. Flood watches and warnings may be needed for late Wednesday
and into Thursday. Tonight`s and tomorrow`s model runs should give a
better indication of where the heavy rain will set up and where
watches and warnings are needed.

.LONG TERM...(Thursday night through Monday)
Issued at 239 PM EDT Mon Jun 26 2017

Good deal of uncertainty with the extended period, especially with
rain chances over the weekend. The combination of surface low
pressure out of the Plains and another shortwave pivoting out of
Canada and into the Great Lakes region is bringing a non-zero chance
of rain for the weekend. The question is when and where, with some
guidance keeping the surface low and bulk of the precip to our
south, and others bringing it right overhead. A second round of
showers will likely follow later in the weekend or early next week
as the axis of H5 troughing clears the area. Will certainly need to
keep an eye on the SE portion of the CWA for rainfall totals, given
the wet antecedent condtions and somewhat anomalous PWAT values
progged not too far to our south. Temperatures are expected to be
near normal, perhaps just a touch below.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 744 PM EDT Mon Jun 26 2017

Band of showers will pivot se-ward, across and out of northern
lower MI this evening. Periods of MVFR conditions are expected.
Otherwise VFR, as low pressure departs Lake Huron and high
pressure moves east from southern MN.

Mainly a nw breeze thru the forecast, though backing a bit more
west by late Tuesday.


&&

.MARINE...
Issued at 239 PM EDT Mon Jun 26 2017

Low end advisory gusts continue across portions of the Lake Michigan
nearshore waters, especially southern areas. Had earlier issued
advisories for the nrn nearshore waters of Lake Huron, as the
gradient appears to tighten up enough tonight. High pressure then
slips SE of the region, allowing winds to become more southerly
through Tuesday and Tuesday night. There is an increase in speed
Tuesday night, but with increasing stability, will not issue any
advisories attm. A much more substantial increase in speed is seen
later Wednesday and Wednesday night, out ahead of a respectable area
of low pressure that will bring showers and thunderstorms. Rainfall
may be quite heavy Wednesday night.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 5 AM EDT Tuesday for LHZ347-348.
LM...SMALL CRAFT ADVISORY until midnight EDT tonight for LMZ342-
     344>346.
LS...SMALL CRAFT ADVISORY until midnight EDT tonight for LSZ321-322.
&&

$$

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



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