National Weather Service United States Department of Commerce

Dangerous Heat Builds and Expands; Critical Fire Weather for the Southwest; Severe Thunderstorms for Plains and Midwest

Dangerous to record breaking heat will build across the center of the nation and slowly build eastward this week. Wildfire conditions remain critical for the Southwest and portions of the Great Basin through Monday. For the northern Plains and upper Midwest, severe thunderstorms with the potential for large to very large hail and severe winds are the primary hazards. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260629_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 06/29 06Z 0.10 3505  69  69  13 0.00
Mon 06/29 07Z 0.15 3305  71  62  13 0.00
Mon 06/29 08Z 0.19 3206  73  61  13 0.00
Mon 06/29 09Z 0.23 3207  74  59  13 0.00
Mon 06/29 10Z 0.23 3208  75  54  13 0.00
Mon 06/29 11Z 0.21 3209  74  48  13 0.00
Mon 06/29 12Z 0.17 3309  73  36  13 0.00
Mon 06/29 13Z 0.14 3309  73  27  13 0.00
Mon 06/29 14Z 0.15 3409  74  25  13 0.00
Mon 06/29 15Z 0.23 3407  75  24  13 0.00
Mon 06/29 16Z 0.52 3307  74  27  13 0.00
Mon 06/29 17Z 0.57 3307  72  35  13 0.01
Mon 06/29 18Z 0.54 3307  68  33  13 0.01
Mon 06/29 19Z 0.76 3307  65  25  13 0.01
Mon 06/29 20Z 0.75 3306  61  17  14 0.00
Mon 06/29 21Z 0.54 3307  57  17  14 0.00
Mon 06/29 22Z 0.26 3306  54  17  14 0.00
Mon 06/29 23Z 0.22 3306  52  23  14 0.00
Tue 06/30 00Z 0.23 3206  51  16  14 0.00
Tue 06/30 01Z 0.35 3106  51   9  14 0.00
Tue 06/30 02Z 0.32 3005  53  13  14 0.00
Tue 06/30 03Z 0.43 2705  57  12  14 0.00
Tue 06/30 04Z 0.44 2605  61  16  14 0.00
Tue 06/30 05Z 0.52 2407  63  12  14 0.00
Tue 06/30 06Z 0.65 2409  63   9  14 0.00
Tue 06/30 07Z 0.78 2511  64  10  14 0.00
Tue 06/30 08Z 0.75 2512  62  14  14 0.00
Tue 06/30 09Z 0.75 2513  64  17  14 0.00
Tue 06/30 10Z 0.80 2613  65  22  13 0.00
Tue 06/30 11Z 0.67 2612  66  32  14 0.00
Tue 06/30 12Z 0.63 2512  69  40  14 0.00
Tue 06/30 13Z 0.58 2512  71  40  14 0.00
Tue 06/30 14Z 0.57 2412  73  54  14 0.00
Tue 06/30 15Z 0.63 2311  75  60  14 0.00
Tue 06/30 16Z 1.36 2311  77  71  14 0.00
Tue 06/30 17Z 1.40 2110  75  76  15 0.00
Tue 06/30 18Z 0.46 1916  73  87  15 0.00
Tue 06/30 19Z 0.90 2017  81  82  15 0.02
Tue 06/30 20Z 1.63 2119  88  84  15 0.02
Tue 06/30 21Z 0.69 2119  85  78  16 0.00
Tue 06/30 22Z 0.64 2221  89  61  16 0.00
Tue 06/30 23Z 0.69 2323  94  51  17 0.01
Wed 07/01 00Z 0.82 2326  95  45  17 0.01
Wed 07/01 01Z 0.84 2426  97  35  17 0.02
Wed 07/01 02Z 0.86 2527  98  36  17 0.03
Wed 07/01 03Z 0.91 2530  97  43  18 0.06
Wed 07/01 04Z 0.79 2630  87  49  19 0.08
Wed 07/01 05Z 0.83 2631  89  43  19 0.02
Wed 07/01 06Z 0.89 2732  91  36  19 0.02
Wed 07/01 07Z 0.83 2831  91  29  19 0.02
Wed 07/01 08Z 0.79 2830  92  19  19 0.03
Wed 07/01 09Z 0.69 2828  90  14  20 0.03
Wed 07/01 10Z 0.59 2825  83  20  20 0.03
Wed 07/01 11Z 0.50 2922  76  25  21 0.02
Wed 07/01 12Z 0.42 2920  67  25  22 0.02
Wed 07/01 13Z 0.36 2918  62  31  22 0.01
Wed 07/01 14Z 0.35 2816  61  33  22 0.01
Wed 07/01 15Z 0.38 2816  62  35  22 0.01
Wed 07/01 16Z 0.38 2815  63  39  22 0.00
Wed 07/01 17Z 0.35 2813  66  37  23 0.00

Run total areal avg QPF for the greens is: 0.50 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1