Area forecast discussion
National Weather Service Grand Rapids Michigan
749 am EDT Tuesday may 21 2013
Latest update...
update/aviation
Synopsis...
issued at 323 am EDT Tuesday may 21 2013
Low pressure over Minnesota this morning will slowly move across the
Great Lakes region through Wednesday night. This system will
produce periods of showers and thunderstorms. Much cooler air will
arrive by Thursday as the rain gradually comes to an end.
The end of the week and into the Holiday weekend looks mainly dry.
Temperatures should gradually warm to around normal values by
Memorial Day.
&&
Update...
issued at 739 am EDT Tuesday may 21 2013
I updated the forecast to better define the timing of the
thunderstorms this afternoon and evening. That is I believe there
is a very limited chance of having additional storms this morning
as there is a large area of upper level convergence behind the
thunderstorm complex that moved through the area early this
morning. As seen on both the water vapor and infrared image loops it
seems to ME the next shortwave will impact the southeast part of Michigan
more so than southwest lower Michigan early to middle afternoon. The
next significant chance of showers and thunderstorms is when the
upper level wave over western Texas at 7 am this morning lifts
northeast toward the western Great Lakes tonight. That means most
of the precipitation will be after midnight.
&&
Short term...(today through thursday)
issued at 323 am EDT Tuesday may 21 2013
A band of showers and thunderstorms will move across the County Warning Area early
this morning. This area was driven by a weakening low level jet as
well as upper divergence from the upper jet. The upper forcing will
also weaken early this morning. So expect the precipitation to gradually
break up and any storms will gradually weaken toward daybreak.
Feel the threat for severe weather has diminished today...although
it can not be completely ruled out. The surface low becomes baggier
as it moves across Wisconsin and no longer supports a focused low
level jet. Meanwhile the right entrance region of the upper jet
will be focused to our south over IL/in. So any strong dynamic
forcing is much weaker today as compared to yesterday. However we
are prognosticated to become rather unstable...especially over the eastern
County Warning Area. The wild card will be how long the debris clouds hold in...and
whether we can realize this instability. If we can break out and
the morning convective leaves a few boundaries...severe potential
will increase especially east of U.S. 131.
Feel any risk of severe storms will wind down quickly this evening
as the surface low brings in deep moisture...but diminishing
instability. Strong indication that a vorticity maximum will rotate around
the upper low and move into lower Michigan late tonight. This should
bring an expanding area of showers and storms to SW Michigan after
midnight...but severe storms are not expected.
The deep moisture lingers over the County Warning Area Wednesday and Wednesday night. We will
have to watch how this unfold as the risk turns to the potential for
heavy rain. If these rains were to focus in one particular area...
localized flooding could occur.
The surface low and it/S cold front finally exits the County Warning Area on
Thursday. Still looks like quite a wet day over the southern County Warning Area.
However clearing should arrive for northern areas by late in the
day. Temperatures will be much cooler...with middle 60s in areas that see
some sun...but only upper 50s in the wetter south.
Long term...(thursday night through monday)
issued at 323 am EDT Tuesday may 21 2013
There are two significant weather issues we are tracking. The frost
issue up north Saturday morning and the threat of showers and
thunderstorms Saturday into Sunday.
The large scale picture features troughs on both coasts over the
weekend with a large scale mean ridge over central North America
from Texas north into central Canada. The Pacific system that
closes off a low over the Pacific northwest sends a shortwave over
over the top of the ridge and creates a wave on the front that if
the European model (ecmwf) from the 12z run were correct would bring rain and the
threat of thunderstorms to the area Saturday into Sunday. The GFS
keeps this system south of the area. Based on continuity over the
past few days I am favoring the dry solution of the GFS.
That would allow for colder temperatures Friday night /Saturday
morning and maintain the threat for frost. It would also mean partly
sunny skies and cool temperature through the Memorial Day weekend.
&&
Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 739 am EDT Tuesday may 21 2013
The convective complex that impacted the area early this morning
is departing the area. I expect mostly middle and high clouds the
rest of the morning. The next convective outbreak should largely
pass east and southeast of this area this afternoon. I put thunderstorms in the vicinity in
the taf sites during the afternoon just in case some think does
develop.
The main upper wave heads toward southwest Michigan after midnight
so I brought rain into the area around 09z with MVFR visibility. Ceilings
will become MVFR too but I through that would wait until it had
been raining for a few hours... thus after 12z.
&&
Marine...
issued at 323 am EDT Tuesday may 21 2013
Southerly flow will gradually weaken over the next couple of days as
a surface low moves toward the lake. However northerly winds will
increase on the back side of the low. We may need a Small Craft Advisory by Thursday.
&&
Fire weather...
issued at 323 am EDT Tuesday may 21 2013
The area will see periods of rain through Thursday. Over an inch of
rain is likely keeping the fire risk low.
&&
Hydrology...
issued at 323 am EDT Tuesday may 21 2013
Periods of heavier rain is expected by late tonight and should
linger until Thursday. If this sets up over the same areas we may
see localized flooding. A Flood Watch may need to be considered if
a focused area of heavy rain is expected.
&&
GRR watches/warnings/advisories...
Michigan...none.
Lm...none.
&&
$$
Update...wdm
synopsis...jk
short term...jk
long term...wdm
aviation...wdm
fire weather...jk
hydrology...jk
marine...jk
