Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/14/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1055 PM EDT Tue Jul 13 2021
A series of weak cold fronts will track east across the area
tonight through Wednesday, bringing scattered showers and
thunderstorms to the area. The best chance for rain will be
Wednesday afternoon. High pressure will bring dry, warm weather
on Thursday, then the next chance of thunderstorms will be
Friday afternoon as another front approaches from the northwest.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
.UPDATE...Line of strong to severe thunderstorms finally
approaching the western Adirondacks from the Tug Hill. In
collaboration with the Storm Prediction Center, we have extended
the Severe Thunderstorm Watch for Herkimer County until Midnight
as the storms will be moving through between 11 PM and 12 AM.
The storms have had a history of wind damage upstream. Farther
south there are additional strong/severe storms moving across
the southern tier, but it is questionable if these storms will
maintain strength before reaching the Mohawk/Schoharie Valleys.
More stable conditions exist across much of the area, with less
than 500 J/Kg of ML CAPE. Likely scenario is convection will
make it into the western half of the area, but should weaken
below severe levels. Will mention chance to likely/categorical
POPs through the early morning hours, with the highest values
north/west of Albany.
.PREVIOUS ...Removed mention of POPs for most of the area
over the next few hours, as one cluster of storms tracked
northward just west of the western Adirondacks and the rest of
the area is devoid of any activity for the time being. Main
concern is a line of strong to severe storms moving NE from
west-central NY and central PA. Despite a more stable
environment across much of eastern NY (and especially western
New England), momentum of the storms may result in some of them
making into mainly the western half of the area around 11 PM to
2 AM. Instability gradient in place from the Hudson Valley
westward through the Mohawk Valley and western Adirondacks. The
greatest MLCAPE around 1500-2500 J/Kg is over central/southern
NY according to SPC Mesoanalysis. CAMs are split on whether
activity holds together, but progressive runs of the HRRR
continue to indicate at least a broken line of showers and
storms moving through much of eastern NY before weakening
considerably. Will continue to monitor trends through the
evening, but went ahead and raised POPs after 11 PM.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
The upper ridge that has been located off the mid- Atlantic
coast for the past few days will continue to be knocked down on
Wednesday as additional short wave energy moves east from the
Great Lakes in westerly flow aloft. Meanwhile, some of the
unstable air that has remained west of our area for the past
couple of days will finally push eastward during the day as the
maritime airmass currently covering eastern NY and western New
England is pushed off to the east. This will set the stage for
another round of showers and thunderstorms on Wednesday, mainly
in the afternoon in association with an eastward moving low-
level trough. MLCAPE values of 1000 to 1500 J/kg will combine
with mid-level flow / deep layer shear of 30 to 35 kts to create
conditions that may support some severe storms during the
afternoon. Meanwhile the atmosphere will remain moist enough,
with precipitable water values greater than 1.50 inches, so that
some storms could produce a flash flood threat, especially
given that much of our area has received heavy rainfall over the
past several days.
High pressure will build east across the area later Wednesday
night and Thursday, setting the stage for a dry, warm day. After
some patchy morning fog, sunshine should allow temperatures to
climb well into the 80s during Thursday afternoon. The next
short wave trough and associated cold front will approach the
region on Friday, accompanied by increasing chances of showers
and thunderstorms. Once again the combination of temperatures
well into the 80s with high dew points will result in ample
instability across the region. Instability plus increasing mid-
level flow associated with the approaching trough will result in
another chance for severe storms Friday afternoon.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The period starts out Friday evening with a warm/moist
southwest flow regime in place across our region, with a
positively tilted upper level trough forecast to be positioned
across the central/upper Great Lakes. At the surface, a nearly
stationary front is expected to be in place across
northern/western NY. Scattered to numerous showers with
scattered thunderstorms could still occur into the evening,
before generally tapering off after midnight. Cannot rule out a
few more showers overnight in the moist environment ahead of the
On Saturday, the upper trough axis will slowly move eastward
into the lower Great Lakes area, while the surface front starts
to push southeast into our region. Anomalously high PWATs around
+1 to +2 STDEV forecast (NAEFS) from around Albany southward
during the day, with expected sufficient instability for
thunderstorms to develop as well. Showers will become likely,
although cloud cover could be a mitigating factor for how
unstable it could get with regards to thunderstorm. If there are
more breaks of sunshine early in the day there could be some
stronger storms. It will be continued humid with dewpoints in
the 60s to lower 70s. Showers and some thunderstorms could
continue into the evening, depending on timing of a lead short
wave moving through. There are some model differences, but
enough consensus to mention scattered showers.
Still looking at chances for additional showers and
thunderstorms on Sunday, as the upper level trough axis finally
moves into the Northeast. The higher moisture anomalies look to
shift south of our region by then, but there should be enough
large scale forcing for at least scattered showers and storms.
It should be cooler as well, with slight below normal
temperatures. Will gradually lower POPs Sunday night as the
trough axis pushes south/east.
On Monday, even though the main upper trough axis should be
east of the region, general troughiness and a possible
disturbance moving through in the northwest flow regime could
result in development of mainly diurnally driven scattered
showers and isolated thunderstorms. Temperatures expected to
warm back to normal levels.
More model differences by Tuesday, but either NW or SW flow
could bring another disturbance and again mainly diurnal showers
and a few thunderstorms. For now will mention highest chances
north/west of Albany, but highly uncertain this far out. Bottom
line is the unsettled/wet pattern we`ve been in looks to
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Low level stratus clouds at MVFR levels remain in place early
this evening, with cigs expected to lower to IFR levels after
dark later this evening into the overnight. With widespread
cloud cover fog should only be intermittent and light, with vsby
possibly lowering to MVFR levels overnight. Will have to watch
for potential scattered showers and even some thunder late
tonight, as a complex of convection approaches from central
NY/PA. Activity should generally weaken, but enough of a chance
to mention VCSH for now. IFR cigs will likely be the main
restriction through much of Wednesday morning.
Conditions should improve to MVFR then eventually VFR by late
Wednesday morning, as the flow becomes more southwesterly
resulting better potential for scouring out the low level
clouds. Then, scattered to numerous showers and thunderstorms
are expected during the mid afternoon through early evening
hours Wednesday. Gusty winds and periods of MVFR (or even brief
IFR) will be possible associated with any TSRA. Will mention
PROB30 for TSRA at all TAF sites.
Winds tonight will be southeast around 3-7 kt, becoming south
to southwest around 5-10 kt by late Wednesday morning. Brief
strong wind gusts will be possible with any TSRA Wednesday
afternoon into the evening.
Wednesday Night: Moderate Operational Impact. Slight Chance of SHRA...TSRA.
Thursday: No Operational Impact. NO SIG WX.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: Moderate Operational Impact. Likely SHRA...TSRA.
Friday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Saturday: High Operational Impact. Likely SHRA...TSRA.
Saturday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Sunday: Moderate Operational Impact. Chance of SHRA...TSRA.
Cloudy, humid weather will persist through tonight with scattered
showers and thunderstorms. A better chance of showers and
thunderstorms will occur on Wednesday as a front moves across the
area. Thursday looks to be a mainly dry day with sunshine returning.
It will be warm and a bit humid, but with lower relative humidity
than prior days. Relative humidity values will rise to 90 to 100
percent tonight, then average around 70 percent on Wednesday.
A Flood Warning remains in effect for Falls Village on the
Housatonic for minor flooding.
Most of the HSA has seen 200-400% of normal precip over the last
week. Scattered showers and thunderstorms are expected tonight,
but the chance of heavy rainfall is low.
Wednesday will feature a better chance of rain, as another
system brings numerous showers and thunderstorms. It will be a
very moist airmass, so locally heavy rainfall is expected in any
thunderstorms. However, the storms should be progressive, which
should mitigate a more widespread flood threat.
River levels remain elevated, and some rises to action stage
will be possible through Wednesday. However, main stem river
flooding is not expected at this time.
Dry weather returns on Thursday.
For details on specific area rivers and lakes, including observed
and forecast river stages and lake elevations, please visit the
Advanced Hydrologic Prediction Service /AHPS/ graphs on our
Area Forecast Discussion
National Weather Service Des Moines IA
647 PM CDT Tue Jul 13 2021
...Updated Aviation Discussion...
.DISCUSSION.../Tonight through Tuesday/
Issued at 258 PM CDT Tue Jul 13 2021
-Wed Morning: Wind Threat Northern Iowa
-Wed Afternoon: Brief Supercell Threat, conditional tornado threat
-Wed Evening: Damaging Wind Threat, conditional QLCS tornado threat
-Greatest Uncertainty: Evolution of afternoon convection
-Some hydro concerns
Today Through Thursday:
Weak ridge axis has pushed across Iowa, and subtle H5 height falls
have started this afternoon with the approaching short-wave pulse. A
cumulus field has been noted on visible satellite imagery, and a few
radar returns have been coming in from northwest Iowa. There is
certainly quite a bit of instability in the area with 1500-2000 J/kg
SBCAPE and about 1000 J/kg MLCAPE. Forcing will not be overly strong
through this evening, and there still appears to be some CIN to
battle. Overall, potential for storms to develop remains low, but if
a storm is able to break through, there is also enough deep layer
shear to help strengthen the storm. Main concern though still
remains with thunderstorm activity on Wednesday.
There are two short-wave troughs to keep track of Wednesday through
Thursday that will bring active weather to the region. The first is
currently along the NE-SD border and propagating east-southeast. The
second vorticity max will develop and move along the NE-KS border,
and this second wave will play a role in deepening a surface cyclone
and developing a warm-sector across central and eastern Iowa. These
two features create the potential for two rounds of convection. To
further add to the challenge, what happens in round one will have
critical implications for round two. First, a discussion on the
first short-wave. Overnight, convergence should increase along and
ahead of this feature leading to convection initiation in
northern/northeastern Nebraska. Most of this should be more
elevated, with a decent warm layer having developed around 900-875mb
capping off anything from the surface. Deep layer shear does not
appear too impressive during the early morning hours, with 0-6km
values only around 20kts. Shear in the effective inflow layer is
also only around 20 kts. With relatively weak deep layer shear,
expect most of the cells to to quickly congeal into a convective
cluster. Mid-level lapse rates along this convective cluster will be
around 7.5 C/km, perhaps a little bit greater, which may allow for
complex to gain considerable depth as it propagates along the short-
wave into Iowa between 10-13z. While not a classic inverted-v
sounding structure near the surface, soundings do favor some higher
dewpoint depressions near the surface and DCAPE values approaching
1000 J/kg. Therefore, this early morning convective cluster does
present a damaging wind threat, especially if strong cold pools
develop. Hodographs ahead of this line do have notable curvature,
with a few models outputting 50-75 m^2/s^2 SRH in the 0-500m layer,
and nearly 100 m^2/s^2 for 0-1km layer. However, don`t anticipate
this line moving anywhere near to estimates of a RM supercell
motion. This coupled, with the surface still being capped off, will
make it difficult to realize any true streamwise vorticity and thus
limit any tornado threat with the morning convective complex in
Iowa. That may change as the line moves into southeast Minnesota and
southwest Wisconsin, where daytime heating could allow surface
parcels to come back into play.
During the late morning and early afternoon, surface cyclone will
continue to deepen over the central Plains and will increase WAA
over Iowa with stronger southerly flow. This will also increase
convergence, especially for areas north of Interstate 80. The
morning convection should clear northern Iowa by 17-18z, which in
theory should leave plenty of time for peak heating to destabilize
the convective boundary layer heading into the afternoon. One
hindrance could be lingering convective debris or stratiform rain
that blocks this. Most of the CAM guidance the past few hours though
does not show much preventing insolation. During the afternoon, HREF
mean SBCAPE values are near 2000 J/kg. On the higher end of the
spectrum, SBCAPE values could reach between 3000-4000 J/kg SBCAPE.
In this strong WAA regime, this is not out of the question. The
other important factor from the previous convection is the placement
of an outflow boundary, and then how quickly this outflow boundary
moves. For areas along and north of Hwy. 30, the surface cyclone may
provide enough convergence where the outflow boundary is not needed
for initiation (though would greatly enhance convergence if
present). For east-central and southeastern Iowa, this outflow
boundary will be needed for stronger forcing. If an outflow boundary
advances southeastward, this will move through a rather potent warm-
sector with increasing shear throughout the day. Assuming that skies
clear up from morning convection, expect round two to initiate with
peak heating, making the threat time around 20z through the rest of
the evening. Unfortunately, there is still a decent amount of
spread in model guidance over the evolution of this second round of
convection, likely sensitive to where an outflow boundary may setup.
Further, this makes the threats hard to point out, as this boundary
will also effect how the low-level hodograph shape evolves. Looking
at recent cycles of the RAP and HRRR, there are two different
hodograph stories, one for north of Interstate 80 and one south.
North of Interstate 80 in the area of previous morning convection,
flow will increase the speed shear, with nearly 40 kts of deep layer
bulk shear. However, in the 0-3km layer, there is not much turning
of the hodograph, with SRH values in the 0-1 km layer barely
reaching 80 m^2/s^2. However, if there is a lingering outflow
boundary hanging around that backs the surface wind, this could
drastically change this picture. Story number 2 for south of
Interstate 80, low-level flow will continue to increase throughout
the afternoon and surface winds back ahead of the surface cyclone.
Hodographs in the lowest levels have considerable turning, with SRH
values in the 0-1 km layer over 150 m^2/s^2. This is also the area
with a more potent warm sector, however, forcing may not be as
strong in this area. With convective initiation after 20z, there
could be some supercells that develop, especially if there is an
outflow boundary where the deep layer shear vector orients
perpendicular to. These supercells could present all threat types.
The tornado threat, especially for north of Interstate 80, will be
conditional on some kind of mechanism being able to turn the
hodograph a bit more. For areas south, the hodographs will already
likely be turning enough in the lowest-levels. In terms of hail, mid-
level lapse rates and deep layer shear will certainly support a hail
threat south of Interstate 80. Most of the forecast area will have
an equal damaging wind threat, with decent low-level lapse rates and
DCAPE values of 1000-1500 J/kg. If supercells develop, it will be
difficult to maintain discrete storms as the LLJ strengthens. This
may be able to initially further loop the low-level hodographs, but
eventually this will force most storms to congeal into a linear
complex. But, this will also increase 0-3km bulk shear, and
depending on how exactly the line develops, could present a linear
tornado threat should this vector orient perpendicular to the line.
The damaging wind threat will then continue into the evening past
00z, and expect the shear environment to be favorable to help
balance and maintain strong cold pools, perhaps even foster the
development of a strong RIJ and generate a bowing line segment.
Eventually the complex will move eastward with the short-wave out of
the forecast area and become the typical summertime Corn Belt MCS.
Stratiform precipitation may wrap around the back side of the
surface low pressure through early Thursday afternoon.
By Friday afternoon an amplified mid-level ridge will be present
with its axis centered over the western third of the CONUS. A trough
will sit off the Pacific Northwest Coast and will send intermittent
short-wave perturbations across Canada. With the upper Midwest being
downstream of the ridge, some of these shortwaves will likely be
able to work their way southeast into Iowa, which will introduce
some rain shower chances throughout the extended portion of the
forecast. Overall flow will be rather weak though across the area,
thus will make it tough for any real organization of anything.
Temperatures will remain seasonable for most of the week under this
.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 641 PM CDT Tue Jul 13 2021
VFR conditions tonight into Wednesday before convection is
possible during the last 12 hours of the TAF period. Hires models
suggest late morning into early afternoon hours for convection and
then a second round late Wednesday evening which will be addressed
in the next TAF issuance. Certainly looks likely to see at least
some MVFR visibility and ceilings b/t 15-22z time frame, but kept
the mention of VCTS attm as duration and timing still
Issued at 258 PM CDT Tue Jul 13 2021
Deep warm-cloud layer processes will allow for thunderstorms to be
efficient rain producers on Wednesday through early Thursday
morning.The highest QPF totals continue to be painted across
northern portions of the forecast area, which is also the area in
need of rainfall and can handle quite a bit before any real flooding
concerns come into play. A few CAMs try to paint as much as 2-4
inches for areas north of Hwy. 20. These amounts are locally
possible, but would not expect this to be widespread. Rural areas
are expected to be okay with heavy rainfall. Urban and developed
areas may see some flooding issues if heavy rain continues. If the
deep layer shear vector ends up orienting parallel to an initiation
boundary, the chance for training storms will increase. At this
time, there is still some uncertainty if this will be the case. The
low-level jet could end up making this happen. This is reflected by
WPCs slight risk for excessive rainfall. Given the dry antecedent
conditions and the overall threat for training storms being
conditional, will not issue a Flash Flood Watch at this time.
However, if mesoanalysis as the event unfolds finds it favorable for
training heavy rain storms, adjustments can be made. Rises on rivers
are possible, and heavy rainfall may result in local creeks and
streams rising to bankfull. Hydrology is not expected to the
greatest problem with this storm event, but will need to be
Area Forecast Discussion
National Weather Service Quad Cities IA IL
621 PM CDT Tue Jul 13 2021
...00Z AVIATION UPDATE...
Issued at 523 PM CDT Tue Jul 13 2021
Area radars showed scattered, elevated showers and isolated
thunderstorms from north central Iowa into western Iowa late this
afternoon. These were associated with an upper level shortwave
moving across central Iowa, interacting with steep mid level lapse
rates and elevated warm advection and moisture return from the
Central Plains. Have updated the forecast to introduce isolated
showers and thunderstorms over east central Iowa late this
afternoon into early evening. Do not have much confidence in how
far east-southeast this activity will reach before dissipating as
it moves away from the axis of higher MUCAPEs over the MO River
Issued at 230 PM CDT Tue Jul 13 2021
The upper low that brought widespread cloud cover to the area over
the past several days has finally moved far away to lead to periods
of sun and warmer weather. This has allowed temps to rise into
the upper 70s to low 80s. It`s also quite humid this afternoon
with dewpoints in the mid 60s to low 70s.
.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 230 PM CDT Tue Jul 13 2021
*Enhanced risk for severe thunderstorms roughly along/north of
highway 30 on Wednesday. A slight risk extends to the south
*Slight risk for flash flooding Wednesday and Wednesday night
north of highway 30 where repeated storms could result in 1-3+
inches of rain for the hardest hit areas.
This Evening into Wednesday Morning
South winds will become steady overnight as low pressure and
organized convection develop in the Central Plains. The first
portion of the night will be quiet with temps falling back into
the 60s and 70s. An increasing southwesterly LLJ may kick off a
few showers or storms well after midnight into early Wednesday
morning, with best chances north of highway 30 and along/west of
the Mississippi River. Coverage with this first round of activity
should remain low. If these storms form, a few could become
strong but organized severe weather is not anticipated.
Wednesday Midday into the Evening
Latest model consensus has a MCS tracking mostly to the north of
the forecast area, across northern IA/southern MN and WI. This
seems to be a reasonable scenario based on 850-300mb mean wind and
forward-prop. Corfidi vectors oriented slightly to the north of
east. With that said, as shown by the 18Z HRRR and other CAM
runs, scattered storms could fire south of the MCS and pose a
severe risk from the mid afternoon into the early evening, mainly
to the north of highway 30. If storms form during the afternoon,
moderate deep layer would be supportive of supercells and all
severe weather hazards. The setup for storms Wednesday night is
discussed in the following section.
.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 230 PM CDT Tue Jul 13 2021
1) Rainy and stormy start to the long term period, with an Enhanced
Risk for Severe Weather on Wednesday and a Marginal Risk on Thursday.
2) Deep ridging takes place over the western United States, slowly
creeping east. This will have the potential to bring above normal
temperatures and drier weather.
Wednesday Night Through Friday...
A humid start to the extended forecast is what we have in store for
us. A surface low pressure system will track towards the northeast,
through out northwestern part of our forecast area. An attendant
cold front will trail it, with a muggy/warm sector in place.
Temperatures will be in the mid 80s, with short term guidance
hinting at dew points possibly reaching the mid 70s ahead of the
front. Wednesday night and into Thursday is also where we will see
the higher PWATs move into the area, where guidance brings in
upwards to 2" PWATs. This will set the stage for the heavy rain
potential with any thunderstorms, which can also lead to potential
flash flood concerns, especially for areas that have seen several
inches of rain in the past couple weeks. As of now, the Weather
Prediction center has us in a Slight Risk for Excessive Rainfall
Wednesday night and into Thursday morning, transitioning to a
Marginal Risk through Thursday.
Also, the Storm Prediction Center has issued an Enhanced Risk (level
3) for severe weather along and north of Highway 30 and a Slight
Risk (level 2) for areas along and north of Interstate 80 Wednesday
evening and through the night, with a Marginal Risk for Severe
Weather once again on Thursday. Out ahead of the front, plenty of
instability will be present, with high moisture and temperatures.
Therefore, thunderstorms are likely, especially Wednesday night,
starting around 7PM CDT. Primary hazards with the storms overnight
will be severe gusts and flash flooding, with the secondary being
isolated large hail. The storms should be relatively scattered,
increasing in coverage overnight. Currently for Thursday, it seems
the best chances will be along and south of a line from Freeport IL
to Fairfield IA, while most of the area north of Highway 34 will
have a chance Wednesday night.
Looking at model soundings, there are some inconsistencies still,
but all favor some sort of severe potential. All hazards will be
possible on Thursday. While soils in the north are very dry, the
ground is very solid, where excessive rainfall rates may quickly
lead to runoff due to poor infiltration.
Keep in mind, the severe potential, let alone thunderstorm potential
on Thursday , will rely on convective debris left over from
thunderstorms overnight Wednesday. If it lasts late through Thursday
morning, this may cut back on potential. Will continue to monitor
and update as confidence increases.
Friday, the cold front will be moving out of the area, but the
warmth and humidity are here to stay. Some guidance is hinting at
the chance for showers and storms to continue through the afternoon
on Friday, since the front isn`t too quick on getting out of the
area. At any rate, the severe threat should be lower than the
previous two days.
Weekend and Beyond...
While all long term guidance seems to stray off in different
directions, they all hint at the large upper ridge in the west
slowly creeping east, with a cut off low showing up in some runs to
our south. This will lead us to more of a dry pattern, with near
normal temperatures settling in the region. With warm and relatively
moist conditions, isolated chances for a pop-up showers or storms
cannot be ruled out. The GFS wants to stall out a front south of our
area, which can act as a mechanism for some further isolated
development. As of right now, the forecast next week seems to be
mostly dry though. The Climate Prediction Center hints at a slight
favorability for above normal temperatures, with below normal
.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
ISSUED AT 620 PM CDT Tue Jul 13 2021
VFR conditions will prevail overnight into Wednesday. Isolated
showers and thunderstorms may impact the CID terminal early this
evening with brief MVFR conditions. Showers and thunderstorms may
also redevelop after 06Z and potentially impact the CID terminal,
but confidence of this occurring is too low to include mention in
the forecasts. Another round of scattered showers and
thunderstorms is looking more likely around midday into the
afternoon hours Wednesday and PROB30 groups have been added to
CID, DBQ and MLI. These storms could potentially produce strong
winds and heavy rainfall, producing at least short periods of
well below IFR.
Area Forecast Discussion
National Weather Service Grand Forks ND
1050 PM CDT Tue Jul 13 2021
Issued at 1008 PM CDT Tue Jul 13 2021
No updates of note to share within the short term forecast.
UPDATE Issued at 659 PM CDT Tue Jul 13 2021
Little change was made to the forecast. Smoke near the surface
continues across the region, although vsbys remain above 5SM.
Thus, keeping it out of the forecast for now as day shift did.
Quiet conditions are expected this evening and tonight with calm
winds and passing clouds/lingering smoke.
Latest HRRR trends show some isolated showers moving over the
international border tonight assoc with a very subtle s/w noted on
WV imagery currently in central MB. Chose to keep out of the
forecast for now due to the lack of impacts and low confidence
owing to weak forcing and dry air currently present over the area;
but will monitor if precip develops with this. Otherwise, the
well defined s/w moving out of the northern High Plains should
start to makes its way eastward into the Dakotas. Still thinking
majority of this precip closer to the surface response will stay
south of the FA.
.SHORT TERM...(This evening through Wednesday night)
Issued at 237 PM CDT Tue Jul 13 2021
Smoke/air quality issues and the chances for precipitation
Wednesday into Wednesday night are the main forecast challenges.
Despite the smoke today, cumulus did manage to form, which was a
first for the past several days. Expect increasing clouds from the
west late tonight, with fairly light winds again. Although the
smoke has been a little more detectable today, visibilities have
remained above 5-6 miles. Therefore will not mention it in the
forecast, unless visibilities get worse than that. On Wednesday
into Wednesday night, the next short wave will cross the Northern
Plains. The best chances for rain will be near the surface front,
will will drape from west to east across central South Dakota into
Southern Minnesota. There could be a sharp northern cutoff to
where this precipitation reaches and where it doesn`t. The GEFS,
Canadian, and ECMWF ensembles show mid range probabilities for
0.10 inches along the ND/SD border into adjacent areas of west
central Minnesota, with the highest probabilities further south.
With the presence of the short wave, just about anywhere across
the FA could see a few showers or rumbles of thunder during the
afternoon into early evening.
.LONG TERM...(Thursday through Tuesday)
Issued at 237 PM CDT Tue Jul 13 2021
Impactful weather chances will revolve around wildfire smoke
transport Thu-Fri followed by increasing heat indices early next
Large ridge setting up to the west of the northern plains will drift
very slowly to the east during last half of the extended fcst period
and should keep the remarkably dry stretch going. Dense smoke from
Canadian wildfires will be an issue at the beginning of the period,
and near surface wind direction will play the critical role for
surface visibility reductions.
Temps by early next week: NBM 90th percentile shows 100-105 degrees
over northern valley, mid 90s for the 50th. And by next Mon/Tue,
some of the 700 mb geopotential height ensembles are registering
values outside of climate reference ranges. If we can reach these 75
to 90 percentile temps, there would be a good chance for some kind
of heat headlines during that time. Lower RHs and smoke will play
vital roles in the ability to achieve these numbers, but mid 90s for
highs certainly seems reasonable right now.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1050 PM CDT Tue Jul 13 2021
VFR conditions will prevail throughout the TAF period. Elevated
smoke with some minor vsby restrictions from near surface smoke
will persist through the TAF period as well. A low pressure system
moves through South Dakota into Minnesota Wednesday bringing an
area of showers and thunderstorms with it. However, there is
fairly high confidence the majority of this precip will remain
south of all TAF sites. There may however be some separate, brief
isolated afternoon showers and thunderstorms Wednesday afternoon
across the entire region that may encounter TAF sites. Confidence
in this activity was low enough to omit the mention of
-SHRA/-TSRA out of the TAF forecast for now.
Area Forecast Discussion
National Weather Service Goodland KS
528 PM MDT Tue Jul 13 2021
.SHORT TERM...(This evening through Friday)
Issued at 210 PM MDT Tue Jul 13 2021
Shortwave trough will eject from the northern Rockies into the
northern High Plains tonight. Local area will be on the southern
fringe of the associated forcing as it shears out. Convection
will develop in the Nebraska panhandle and coalesce into an MCS in
central Nebraska, with some of this activity possibly clipping
southwest Nebraska later tonight and into the overnight hours. A
stationary front meandering near the Kansas and Nebraska border
area may also serve as a more localized forcing mechanism earlier
in the evening, where latest HRRR run is developing an isolated
storm. Instability at that time will be around 1500 j/kg MLCAPE
but with rapidly increasing CIN. If a storm manages to develop
near the front and remains rooted in the boundary layer, deep
layer shear of 30-40kts may be enough for a severe storm or two
capable of producing large hail and damaging winds. Further south
and west, may also see a broken line of storms coming out of
Colorado, decaying as it approaches the Kansas border area, with
a risk of gusty winds as they do so. Low temperatures will range
from the lower 60s to lower 70s.
Cold front will enter northwest part of the area Wednesday morning
and by 21z be roughly along a Norton to Tribune line. A few
isolated showers/thunderstorms may develop along the front prior
to 21z, but most of the convection will initiate after 21z in the
southeastern part of the forecast area along the front.
Environment along/ahead of the front will be characterized by
SBCAPE of up to 1500 j/kg and deep layer shear of 15-20kts. While
an isolated severe storm appears possible, lack of shear will be a
limiting factor for storm organization. Other storms may develop
in the higher terrain to the west in the post frontal upslope
regime, but deep layer shear is only marginally better and
instability slightly lower. As a result, expecting only a marginal
risk of severe storm across the area on Wednesday, probably along
the front in the afternoon being the best location. Highs will
range from the middle 80s well behind the front to the upper 90s
ahead of it and lows Wednesday night cooling off to the upper 50s
to lower 60s.
On Thursday, the area will be post frontal in the low levels with
a weak northwest flow aloft downstream of the western ridge axis.
Does appear to be a weak impulse in the upper flow, which
combined with the upslope in the low levels typically results in
convection on the higher terrain of eastern Colorado. Instability
axis is forecast to be just west of our area, Limon to Akron, with
deep layer shear around 40kts. May see an isolated severe storm
or two develop in that environment, but with mean storm motions
southeast and right movers southwest, appears most storms will
stay west of the area, but there is a chance some could reach
western portions of Kit Carson and Cheyenne counties by later in
the afternoon and early evening. High temperatures will be in the
middle 80s and lows Thursday night in the upper 50s to lower 60s.
By Friday, heights will be rising as the upper ridge nudges
eastward across the Rockies and adjacent plains. There is a hint
of a weak impulse coming through the ridge axis Friday afternoon
which when combined with moderate instabilty appears to be enough
for isolated showers and thunderstorms. Deep layer shear is
forecast to be around 20-30kts, marginal for organized updrafts,
and combined with the weak forcing not expecting severe storms at
this time on Friday. High temperatures will be around 90 and lows
Friday night in the 60s.
.LONG TERM...(Saturday through Tuesday)
Issued at 213 PM MDT Tue Jul 13 2021
The long term period is currently forecasted to have conditional
thunderstorm chances throughout the period. Temperatures are
currently forecasted to be in the 90`s over the weekend before
dropping into the 80`s to start the week. However, there is
uncertainty regarding whether or not that will happen.
Going into the weekend, the ridge over the 4 corners region is
forecasted to expand and amplify to cover most of the Western CONUS
and portions of Central Canada. This would have the area shift to
more of a northerly flow aloft and weaken the flow a bit. Both of
these modifications would lower storms chances as shear decreases
and shortwave support stays further north. Near the surface,
relatively high pressure will setup over the Plains. This will also
lower storm chances a bit, but could also allow a cooler air mass to
mix into the area.
With these features in mind, forecast calls for high temperatures to
reach the 90`s along with dewpoints reaching the 60`s and maybe even
70`s in the eastern portion of the area as surface southeasterly
flow helps advect moisture into the area. It is still uncertain if
the cooler air mass to the northeast will intrude into the area or
if the higher dewpoints will limit how high temperatures go. But
given that this pattern has been similar to some of the patterns of
the previous weeks, still favoring warmer temperatures in the
forecast compared to most guidance. If the warmer temperatures
prevail in the mid to upper 90`s and dewpoints remain above 60,
could have days this weekend with heat index values reaching 100+.
Will continue to monitor. As for storm chances, available moisture
throughout most of the lower and mid parts of the atmosphere and the
chance for a low pressure system off the front range give the area a
chance for thunderstorms during the afternoon/evening hours in spite
of the surface high and ridge aloft nearby. But have kept chances at
or below 25% given that it is a conditional threat that depends on a
feature such as a surface front or low pressure system forming and
moving through the area. Stand alone airmass thunderstorms could be
possible given the moisture available, but the chance remains low
The beginning of the next week has some uncertainty as to how the
features will evolve and how much the surface high pressure will
move west. The deterministic GFS has diverged a bit from other
guidance, but ensemble data has the same general pattern with the
ridge staying in place while remaining amplified into Canada.
However, guidance (especially the GFS) is hinting at lower heights
or even a cut-off low undercutting the ridge. This seems unlikely,
but would lower temperatures compared to the weekend. Currently have
temperatures around 90, but may need to warm if the undercut doesn`t
happen. Otherwise, conditional chances for thunderstorms remain in
the forecast to start next week.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 528 PM MDT Tue Jul 13 2021
Vfr conditions are anticipated through the TAF period at both
KGLD and KMCK terminals. A few thunderstorms may develop in
eastern Colorado and enter the region from the west this evening;
however, confidence in storms impacting either site was not high
enough to insert a mention at this time. If storms would track
near a terminal, brief breezy winds and reduced visibilities would
likely occur. Otherwise, southerly winds prevail tonight prior to
a cold front entering the region Wednesday morning and shifting
winds to the north. Additionally, LLWS is anticipated for a few
hours at KMCK (roughly 07 to 12z) due to a low level jet.
Area Forecast Discussion
National Weather Service New York NY
1029 PM EDT Tue Jul 13 2021
A warm front will move lift north of the waters tonight into
Wednesday morning. Offshore high pressure gradually shifts
farther out into the Atlantic Thursday through Friday. A cold
front slowly approaches going into the weekend with the front
moving into the region towards the latter half of the weekend.
The front is forecast to slowly move east of the region early
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Areas of drizzle have developed along the coast with lower
stratus and fog, so added to forecast until the warm front moves
through the region. And continued with areas of fog. Mesoscale
models such as HRRR and NARRE are showing the possibility of
dense fog tonight. However, not enough confidence to go with
dense fog advisory yet as there is still a lot of ambient cloud
cover that may inhibit how dense the fog gets. Temperatures were
slightly lowered as well compared to previous forecast.
A warm front to the south of the area will move north overnight.
Fog and low stratus will continue as the warm front will still
be situated to our south and onshore flow continues. Winds will
become light and variable as well, so there won`t be much chance
for the fog to mix out, even as the warm front lifts north.
There remains the possibility some of the fog will become dense.
Otherwise, as the front moves north, instability increases. So, it
looks like the area will transition from light showers and drizzle
to showers and thunderstorms from south to north. Lifted indices by
early morning -1 to -4, so would not be surprised if there was a
strong storm that moves through. Any convection overnight looks to
be elevated, with Showalter Indices lowering to -2 to -3.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
The forecast area will be warm sectored on Wednesday. This will
allow for a much warmer and continued humid day. Temperatures look
to top out in the upper 80s to around 90 for much of the region.
Heat index values of 95-99 are possible across NYC, northeast New
Jersey, portions of Long Island, and southern portions of the Lower
Hudson Valley. However, given the uncertainty in cloud forecast and
in heat index values for Thursday, decided to hold off on Heat
Advisories for now.
A surface trough will develop in the afternoon, allowing convection
to develop during the afternoon and early evening hours. Conditions
will be rather unstable, with steep low level lapse rates along with
1000-3000 J/kg of CAPE Wednesday. The warm frontal boundary will
still be in the vicinity, which will help provide lift for storm
development. Finally, there should be enough moisture with dew
points in the upper 60s to lower 70s and PWATS in the 1-2 inch
range. Some storms tomorrow could become strong to potentially
severe, with the main threat being damaging winds. SPC has placed
much of the forecast area in a marginal risk for severe storms.
Showers and thunderstorms should end after sunset Wednesday evening,
with dry conditions returning everywhere after midnight.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
For Thursday, ridge in mid levels will be flatter and centered
across Western Atlantic where it will remain through early
Saturday. The local region will be on the northwest periphery of
the ridge. Thursday and Friday have subtle shortwaves embedded
along the northwest periphery of the ridge, with the one on
Friday getting relatively closer to the region from the west.
Increasing SW low level flow will allow for a increasingly warm
and humid airmass to develop within the region. Models convey a
consensus of 850mb temperatures near 16 to 18 degrees C Thursday
and near 18 to 19 degrees C Friday. Forecast dewpoints will be
in the lower 70s. High temperatures are forecast to be in the
upper 80s to lower 90s both Thursday and Friday. Friday is
forecast to be a few degrees warmer than the previous day.
Forecast heat indices are forecast to reach mid to upper 90s for
much of Northeast NJ, NYC, Western Long Island, Rockland
County, Westchester County and Southern Fairfield on Thursday
and then for the entire region for Friday in the 95 into lower
100s range. Some isolated 105 degree heat indices on Friday will
be possible in the vicinity of NYC.
Weather is forecast to remain mainly dry Thursday through Friday
morning with chances of showers and thunderstorms Friday afternoon
into Friday night with the approach of a trough ahead of the cold
For Saturday, the mid level ridge will be farther offshore and a
deeper mid level trough moves into the local area. A cold front at
the surface will be approaching and eventually moving into the
region towards the latter part of the weekend. 850mb temperatures
are forecast to be near 18 to 19 degrees C Saturday from a model
consensus. The trough moves farther southward into the region
Sunday. The height falls this weekend aloft will allow for
convection to more easily develop and increase in coverage
especially with the cold front moving into the region. 850mb
temperatures lower a few degrees Sunday compared to the previous
day. At the surface, chances of showers and thunderstorms are in the
forecast for the weekend with highest likelihood Saturday afternoon
into Saturday evening and then Sunday afternoon into Sunday evening.
Highs forecast are in the mid 80s to near 90 for Saturday and low to
mid 80s for Sunday. Temperature forecast is of low confidence due to
the increasing amount of showers and thunderstorms expected.
Temperatures could be cooler than forecast depending on the duration
and frequency of shower and thunderstorm activity. See hydro section
for more details this weekend on potential hydrology issues for
possible minor flooding with thunderstorms.
For early next week, the trough axis will be near the local region
and is expected to move east of the region next Tuesday. At the
surface, the cold front is eventually expected to move across Monday
but may linger nearby going into Tuesday. Highs forecast stay mainly
in the 80s with chances of showers Monday but only a slight chance
of showers next Tuesday. Not as much instability is forecast so
thunderstorms for this time period are a slight chance.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
A frontal boundary will remain nearly stationary just south and
and west into late tonight/toward sunrise Wednesday. The front
then moves slowly north as a warm front through Wednesday
IFR to LIFR through the overnight, with local VLIFR possible in
fog and stratus. Conditions slowly improve around sunrise with
the approach of the warm front, becoming VFR late morning into
the early afternoon, west to east. There is uncertainty with the
timing of the improvements and the movement of the warm front.
Showers and thunderstorms late afternoon into the early early,
mainly from the New York City terminals and west and north,
could produce local MVFR to IFR conditions.
Easterly winds, generally under 10kt, become west to southwest
Wednesday morning as the warm front moves through the terminals.
Along the coast a midday afternoon sea breeze is possible, with
winds S to SSW.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Amendments likely for timing of changing flight categories as
ceilings and visibilities lower through tonight, and then for
improving conditions Wednesday morning. There is uncertainty
with how low conditions will become overnight, especially for
visibilities with the chance of visibilities 1/2 to less than
1/4SM at times. Areal coverage and timing of thunderstorms
Wednesday afternoon is uncertain with a PROB30 group at this
.OUTLOOK FOR 00Z THURSDAY THROUGH SUNDAY...
.Wednesday evening...Showers and thunderstorms possible with
local MVFR/IFR, mainly north and west of NYC terminals.
.Friday-Saturday...Mainly VFR. A chance of showers and
.Sunday...MVFR/IFR possible in showers and thunderstorms.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90
Patchy fog is possible over all waters tonight, limiting
visibility to 1 to 3 NM. There is the potential that the fog
will become more widespread and dense, but confidence was not
high enough yet to issue a Marine Dense Fog Advisory.
Sub-SCA conditions expected Thursday through the weekend with a
relatively weak pressure gradient in place.
Showers and thunderstorms overnight through Wednesday night
should move through quickly enough, so flash flooding is not too
much of a concern, though minor flooding is possible,
especially given antecedent wet conditions.
Concerning period is for the upcoming weekend, some factors
such as parallel flow low to mid levels showing training of
cells, plus PWATS near 2 inches point to possible minor
flooding with any thunderstorms.
There is a moderate risk of rip currents at the ocean beaches
on Wednesday but low risk of rip currents at the ocean beaches
on Thursday. Surf height of around 3 ft in the ocean on
Wednesday is expected to lower to around 2 ft on Thursday. Winds
will remain generally light near 5-10 kt Wednesday through
The monthly rainfall total for July at Central Park is 8.49
inches. With more than half the month to go, this is already the
7th highest July rainfall of record for the Park.
The all-time record July rainfall for the Park is 11.89 inches,
set in 1889. The monthly record could be in jeopardy later this
month given a unanimous consensus of the latest
GFS/ECMWF/Canadian model long-range ensemble forecasts.
Area Forecast Discussion
National Weather Service San Diego CA
118 PM PDT Tue Jul 13 2021
High pressure aloft will slowly weaken over Southern California
through Friday as a trough digs south along the West Coast. This
combination will bring cooling inland, gusty west winds through the
desert passes, and maintain the marine layer over coastal and
western valley areas with seasonal temperatures. Moisture aloft will
continue an isolated thunderstorm threat over mainly the San
Bernardino Mountains and deserts this afternoon. The subtropical
ridge is forecast to rebuild again early next week, but farther
north, over the northern Rockies. This could send a deeper Monsoonal
push into Southern California beginning on Sunday. Showers and
thunderstorm chances will be increasing next week if this pattern
remains on track.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Showers and isolated lightning strikes were evident all morning over
the high deserts to the northeast of the forecast area. Some of
these developed south into the San Bernardino Mountains around
midday with brief heavy rain, small hail, and strong wind gusts.
This activity should settle down after peak heating of the day. The
onshore sfc pressure gradients were increasing and supporting SW
winds of 25-30 MPH and gusts 35-40 MPH near the passes. It was a
little hotter in the I.E. midday, which could be enough to drive
some late day convective development over the Elsinore convergence
zone as well, but the chance looks small at this point.
High pressure aloft over the Southwest will weaken through Friday,
allowing a trough to slip down the West Coast. This combination will
result in stronger onshore flow and more cooling inland as the
marine layer continues to moderate coastal and western valley areas.
Moisture at high levels in the atmosphere will persist with clouds
at times, but the isolated thunderstorm threat will decrease after
Over the coming weekend, the subtropical ridge will begin to rebuild
and should find itself with a strong 598DM center near the Great
Salt Lake by Monday. This position farther to the north, should
allow the circulation around it, to better guide Gulf of Mexico
moisture into SoCal next week. Showers and thunderstorms could begin
as early as Sunday, but timing of this activity over SoCal is
tenuous at best due to the uncertainty of easterly wave timing, and
convective interactions that are likely to develop upstream. The
bottom line here is that the majority of the ensemble members of
both the GFS/EC are indicating some precipitation across SoCal early
next week. This is echoed by the NBM 24-hr probability of measurable
Until then, we may still have isolated shwrs/tstms over, mainly the
San Bernardino Mts and portions of the high desert this afternoon.
Several HRRR model runs have depicted cells in these areas today,
but despite lingering mid-level moisture, they do not for tomorrow.
Perhaps it is the lack of the weak deformation zone aloft tomorrow,
but stability increases and no convection is generated, so it has
been left out of the forecast for the next few days. Deepening
southwest flow aloft and drying through Saturday, should trend the
chance for thunder lower anyway.
132000Z...Coast/Valleys...Areas of low clouds will begin to move
back into the coastal areas after 14/00Z with bases 700-1500 ft MSL
and tops to 2000 ft MSL, locally spreading up to 15 mi inland by
Wednesday morning. Ceilings will impact KSAN/KCRQ/KSNA as normal.
Otherwise VFR conditions are expected.
Mountains/Deserts...Isolated TSRA have developed over the San
Bernardino County mountains, and will persist through sunset.
Isolated TSRA could impact the High Desert as well. Outflow winds
with sfc gusts to 35 kt possible VCTY TSRA, along with brief heavy
rainfall. SHRA/TSRA dissipating by 14/02Z. TSRA development is not
No hazardous marine conditions are expected through Sunday.
Elevated surf of 3-4 ft with sets to 5 ft will persist for the
beaches of Orange and northern San Diego Counties generally north of
Encinitas through Friday. Hazardous swimming conditions are expected
due to a high risk of rip and longshore currents.
Isolated thunderstorms this afternoon, mainly near the San
Bernardino mountains with dry lightning strikes and gusty, erratic
downdraft winds possible. Drying is then expected through Saturday
with a greater influx of monsoonal moisture for Sunday through much
of next week.
Stronger westerly winds 25-35 MPH with gusts 40-50 MPH are possible
Wednesday and Thursday afternoons and evenings through and below
the desert passes.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.