Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 221104
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
604 AM CDT SUN MAY 22 2016

.SHORT TERM...(Today and tonight)
Issued at 439 AM CDT Sun May 22 2016

The main issue for the short term forecast is chance for
thunderstorms/severe weather tonight.

The omega blocking pattern persists today with a western trough and
a the ridge over the central United States as a jet streak stretches
from the central Rockies into the northern Plains will stream nearly
parallel with a surface cold front, with a warm front/dry line
extending south along the front range of the Rockies from Wyoming to
New Mexico.

As was long expected, thunderstorms should develop along the front
range surface boundary by afternoon as an impulse is ejected
northeast out of the base of the western trough. Convection should
develop along and help propagate east the cold front/dryline, but
slowly, due to the nearly parallel upper level flow. There will be
more than enough instability and bulk shear to produce severe
weather at initialization. There will be a period during the late
afternoon and early evening that tornadoes will be possible, but
this wanes quickly later in the evening.

We currently have some tornadoes mentioned in the HWO, which I will
include since SPC keeps our western CWA in the 5% area, but this is
way more likely to the west of the CWA, and I would not be surprised
at all if we had no tornadic activity.

As storms migrate east, they will move into lower deep layer shear
as instability decreases. Storms will probably fill in to form a
quasi-linear mesoscale convective complex that will not have a
strong push to the east, considering the parallel flow to the
surface front. This will have good potential for some heavy
rainfall. The storms will eventually get far enough east to tap into
the expected strong low-level jet and could actually strengthen a
bit. I think our biggest threat for any severe weather will be wind
as the squall line moves through, and only a minimal threat for
large hail and tornadoes for the most part.

I went pretty close to superblend for temperatures, but I tweaked
the POPs down to mostly slight chance for today, and increased POPs
significantly late tonight as ensembles indicate.

.LONG TERM...(Monday through Saturday)
Issued at 439 AM CDT Sun May 22 2016

The long term is an active pattern littered with thunderstorm
chances everyday. The most notable day for this forecast period is
definitely Tuesday due to the high confidence for severe weather.
Confidence beyond Tuesday dwindles for severe weather. That being
said, Tuesday will be the focus of this discussion.

In the upper levels we will be under southwesterly aloft with no
dominant feature to really speak off besides small embedded impulses
ejecting out over the plains. At the surface, a low will develop
across western parts of the Central Plains and nose its way
into/near the forecast area Tuesday afternoon. The placement of the
surface low and the associated boundaries will be the biggest factor
in severe weather development and coverage across our forecast area.
Current thinking is it will nose up across western/southwestern
portions of the forecast area. There is significant instability
around in the afternoon across the forecast area where the NAM and
GFS indicate most unstable values around 5000 J/Kg. Bulk shear (0-6
km) values are around 45-50 knots. The ingredients for strong
rotating updrafts are going to be in place. Low level (0-1 km)
helicity values are not overly impressive, but with the surface low
so close and the chance for boundaries (warm front) over the
forecast area, a tornado threat cannot be ruled out at this time.
However, the main threats will likely be significant hail (2+
inches) and damaging wind speeds. Depending on where the surface low
and associated boundaries end up, the threat for tornadoes could be
more of an issue. There is a good chance there will be at least a
few supercell thunderstorms around the forecast area on Tuesday, and
severe weather will likely be a threat. This is a day to watch as we
move forward because the forecast can change, but the ingredients
are currently there which warrant the mention for severe weather at
this time with high confidence.

Normal temperatures for this time of year range around the mid to
upper 70s, while lows range around the low to mid 50s. Overall,
temperatures are going to be near or above normal everyday in the
long term.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Monday morning)
Issued at 559 AM CDT Sun May 22 2016

One concern is low-level wind shear for the first couple of hours.
Also, some storms are possible overnight, but ceilings are low
confidence. Overall a low-confidence forecast for ceilings as
models have been poor for the past several days. Lower ceilings
should nudge east this morning, but as in the past, could have
some trouble getting farther east.

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

$$

SHORT TERM...Heinlein
LONG TERM...Guerrero
AVIATION...Heinlein



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