Date:
Run:
Sector:
SPC Guidance
Probabilistic
4-hr HREF/SREF Calibrated:
[info]
At every grid point for the valid forecast hour, two probabilities are paired:
1. Probability of UH ≥ 75 m2/s2 over the previous 4 h (from the HREF)
2. Probability of environmental field(s) meeting a threshold over the previous 4 h (from the SREF; see table below)
The historical frequency of a hazard report occurring within 25 miles of that grid point and within the 4-h period for that forecast pair of probabilities is substituted as the 4-h calibrated hazard probability.

HazardSREF Conditions
HailMUCAPE ≥ 1000 J/kg, Eff. Shear ≥ 20 kt
WindMUCAPE ≥ 250 J/kg, Eff. Shear ≥ 20 kt
24-hr HREF/SREF Calibrated:
[info]
Uses the 4-h hazard probability forecasts that cover the 24-h convective day (i.e., 12z-12z). At every grid point, the cumulative sum of the 4-h probabilities and the maximum 4-h probability are paired. The historical frequency of a hazard report occurring within 25 miles of that grid point and within the 24-h period for those 4-h calibrated hazard probabilities is substituted as the 24-h calibrated hazard probability.
24-hr STP Calibrated:
[info]
A distribution of STP is formed for each gridpoint from points where UH exceeds the 99.99th percentile (within each member's climatology) within a 40 km radius. The 75th percentile of STP from that distribution is then assigned to each point at each hour, and then the maximum daily STP value for each point is used to assign a probability based on the climatological frequency of a tornado given a right-moving supercell and an STP value for each ensemble member. The mean at each point is taken across the members, and then a Gaussian smoother with σ = 50 km is applied.
Synoptic
Upper Wind/Height
500 mb Height/Wind:
[info]
Height and temperature fields are smoothed by interpolating to a 1° grid
700 mb Height/Wind:
[info]
Height and temperature fields are smoothed by interpolating to a 1° grid
850 mb Height/Wind:
[info]
Height and temperature fields are smoothed by interpolating to a 1° grid
Surface
2 m AGL Temperature/MSLP/Wind:
[info]
MSLP field is smoothed by interpolating to a 1° grid
2 m AGL Dew Point/MSLP/Wind:
[info]
MSLP field is smoothed by interpolating to a 1° grid
Severe
Instability
Surface Based CAPE:
Most Unstable CAPE:
[info]
The maximum CAPE value is chosen from among parcels originating from the surface and 6 mixed layers in the lowest 180 hPa AGL (0-30 mb AGL, 30-60 mb AGL, 60-90 mb AGL, 90-120 mb AGL, 120-150 mb AGL, and 150-180 mb AGL). The most unstable individual parcel in this layer may have somewhat larger CAPE in some situations.
Shear
0-3 km SRH:
0-1 km SRH:
Winter
Precipitation Type
1-hr QPF and Precip Type:
[info]
Using a priority list of (1 - freezing rain, 2 - snow, 3 - rain), a type is chosen if more than half of precipitating ensemble members indicate the type has occurred over the past hour; if no category reaches that threshold, then the type is labeled mix
Snow
1-hr Snowfall:
[info]
For each ensemble member, the precipitation falling during each 1-hour period is assumed to be *all snow* if the member indicates that *any snow* has occurred during the period (overestimation can thus occur during mixed precipitation). Uses WPC forecast snow-to-liquid ratio (SLR) when available, or 10:1 SLR otherwise.
12-hr Snowfall:
[info]
For each ensemble member, the precipitation falling during each 1-hour period is assumed to be *all snow* if the member indicates that *any snow* has occurred during the period (overestimation can thus occur during mixed precipitation). Uses WPC forecast snow-to-liquid ratio (SLR) when available, or 10:1 SLR otherwise.
24-hr Snowfall:
[info]
For each ensemble member, the precipitation falling during each 1-hour period is assumed to be *all snow* if the member indicates that *any snow* has occurred during the period (overestimation can thus occur during mixed precipitation). Uses WPC forecast snow-to-liquid ratio (SLR) when available, or 10:1 SLR otherwise.
Fire
Indices
Fosberg Index:
Surface Fields
10 m AGL Wind (Hourly Max):
Relative Humidity:
Combined Probabilities
Relative Humidity and Wind:
Precipitation
QPF
1-hr QPF and Precip Type:
[info]
Using a priority list of (1 - freezing rain, 2 - snow, 3 - rain), a type is chosen if more than half of precipitating ensemble members indicate the type has occurred over the past hour; if no category reaches that threshold, then the type is labeled mix
3-hr QPF:
6-hr QPF:
24-hr QPF:
[info]

Conceptually, PMM (probability-matched mean) is a variation of the ensemble mean with the original ensemble amplitude restored. At each grid point, the ensemble mean value is replaced with a value from the full distribution of individual member forecasts whose rank matches the point's rank within the ensemble mean distribution. See Ebert (2001, MWR) for more details.

LPMM (localized PMM) is a new technique from Clark (2017, WAF) wherein the PMM calculation is restricted to grid points inside some radius of influence, preventing precipitation in geographically distant areas from influencing the local value. On this site, we use r=110 km.

Storm Attributes
Reflectivity:
[info]
Instantaneous composite reflectivity
3-hr max Reflectivity:
[info]
Maximum reflectivity at 1 km AGL
24-hr max Reflectivity:
[info]
Maximum reflectivity at 1 km AGL
Updraft Helicity
3-hr max Updraft Helicity (2-5 km):
24-hr max Updraft Helicity (2-5 km):
Updraft
3-hr max Updraft:
[info]
Column-maximum updraft below 100 hPa for HRW members; below 400 hPa for NAM members
24-hr max Updraft:
[info]
Column-maximum updraft below 100 hPa for HRW members; below 400 hPa for NAM members
10 m Wind
3-hr max Wind Speed:
[info]
Maximum 10 m AGL wind speed coinciding with composite reflectivity >20 dBZ (wind in other areas is ignored)
24-hr max Wind Speed:
[info]
Maximum 10 m AGL wind speed coinciding with composite reflectivity >20 dBZ (wind in other areas is ignored)
Member Viewer
Reflectivity:
[info]
Composite reflectivity
-
SPEED:
+
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Product Overlays
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• 500 mb height, ens mean
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SPC Outlooks
?

Primarily intended for post-event verification. Outlooks are overlaid which match the plotted forecast data temporally and were issued around the time the HREF run became available.

The following tables indicate the correspondence between HREF forecast hours and overlaid outlook products (pending availability).

00z HREF
Forecast HourConvectiveFire
1-1201z SWODY1N/A
13-3606z SWODY107z FWDDY1
12z HREF
Forecast HourConvectiveFire
1-2413z SWODY117z FWDDY1
25-3607z SWODY2N/A
SPC Categorical
SPC Hail
SPC Wind
SPC Fire
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h
• HREFv2 is an operational version of SSEO
?
The High Resolution Ensemble Forecast version 2 (HREFv2) is an operational version of the SPC Storm Scale Ensemble of Opportunity (SSEO). It was developed at the NCEP/Environmental Modeling Center (EMC) and is run daily at 00, 06, 12, and 18 UTC by NCEP Central Operations (NCO). This page displays the 00 UTC and 12 UTC cycles only, and uses a 12-h time-lagged NAM Nest member rather than a 6-h time-lagged NAM Nest member. This prototype page replaces the previous SPC SSEO web page.
• Neighborhood probability details
?
Neighborhood (nh) probabilities (NP) are calculated on the 3-km HREF grid. The neighborhood is a box specified by its radius; if r=40 km, the neighborhood is an 80x80 km box centered on the grid point. Grid point probabilities for exceeding the threshold within the neighborhood are calculated at each point. After these grid point probabilities are calculated, a Gaussian smoother is applied with σ=40 km. The smoothed NP field is plotted on this site.
• HREF members
• HREF/SREF Calibrated Guidance FAQ
• [Close]
MemberICs/LBCsMicrophysicsPBLGrid spacingVert. levelsTime step
HRW NSSLNAM/NAM -6hWSM6MYJ3.2 km4019.1 s
HRW NSSL -12hNAM/NAM -6hWSM6MYJ3.2 km4019.1 s
HRW ARWRAP/GFS -6hWSM6YSU3.2 km5018.9 s
HRW ARW -12hRAP/GFS -6hWSM6YSU3.2 km5018.9 s
HRW NMMBRAP/GFS -6hFerrier-AligoMYJ3.2 km506.6 s
HRW NMMB -12hRAP/GFS -6hFerrier-AligoMYJ3.2 km506.6 s
NAM CONUS NestNAM/NAMFerrier-AligoMYJ3 km606.25 s
NAM CONUS Nest -12hNAM/NAMFerrier-AligoMYJ3 km606.25 s
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