NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260706_1200
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 07/06 12Z 0.15 1407  83  22  13 0.00
Mon 07/06 13Z 0.21 1410  79  18  13 0.00
Mon 07/06 14Z 0.23 1411  76  18  13 0.00
Mon 07/06 15Z 0.29 1311  75  19  13 0.00
Mon 07/06 16Z 0.38 1311  76  20  13 0.00
Mon 07/06 17Z 0.89 1311  79  25  12 0.00
Mon 07/06 18Z 1.82 1411  77  26  12 0.00
Mon 07/06 19Z 1.74 1412  75  25  12 0.00
Mon 07/06 20Z 2.21 1412  76  26  12 0.00
Mon 07/06 21Z 1.35 1412  77  28  12 0.00
Mon 07/06 22Z 1.00 1412  76  30  12 0.01
Mon 07/06 23Z 0.54 1314  74  41  12 0.00
Tue 07/07 00Z 0.42 1317  71  46  13 0.00
Tue 07/07 01Z 0.44 1320  64  45  13 0.00
Tue 07/07 02Z 0.40 1321  60  46  13 0.00
Tue 07/07 03Z 0.38 1422  58  45  13 0.00
Tue 07/07 04Z 0.34 1421  59  44  14 0.00
Tue 07/07 05Z 0.30 1420  62  46  13 0.00
Tue 07/07 06Z 0.28 1419  65  45  13 0.00
Tue 07/07 07Z 0.29 1318  69  38  13 0.00
Tue 07/07 08Z 0.30 1317  73  39  13 0.00
Tue 07/07 09Z 0.33 1217  76  47  13 0.00
Tue 07/07 10Z 0.36 1218  76  56  13 0.01
Tue 07/07 11Z 0.37 1218  74  60  13 0.01
Tue 07/07 12Z 0.43 1119  74  60  13 0.02
Tue 07/07 13Z 0.44 1020  75  60  13 0.01
Tue 07/07 14Z 0.46 1021  77  70  12 0.01
Tue 07/07 15Z 0.49 1021  78  74  12 0.01
Tue 07/07 16Z 0.48 1020  78  72  12 0.02
Tue 07/07 17Z 0.50 0919  81  67  12 0.01
Tue 07/07 18Z 0.53 0918  82  61  12 0.01
Tue 07/07 19Z 0.65 0817  81  56  12 0.00
Tue 07/07 20Z 0.80 0817  83  50  11 0.00
Tue 07/07 21Z 0.77 0817  82  46  11 0.00
Tue 07/07 22Z 0.58 0818  82  45  12 0.00
Tue 07/07 23Z 0.49 0917  82  46  12 0.00
Wed 07/08 00Z 0.41 0916  81  41  12 0.00
Wed 07/08 01Z 0.35 0914  79  33  12 0.00
Wed 07/08 02Z 0.31 0813  78  23  12 0.00
Wed 07/08 03Z 0.30 0712  75  15  12 0.00
Wed 07/08 04Z 0.27 0711  72  14  12 0.00
Wed 07/08 05Z 0.22 0510  68  13  12 0.00
Wed 07/08 06Z 0.19 0410  65  11  13 0.00
Wed 07/08 07Z 0.14 0308  64  10  12 0.00
Wed 07/08 08Z 0.10 0208  63  12  12 0.00
Wed 07/08 09Z 0.12 0209  62  10  12 0.00
Wed 07/08 10Z 0.11 0209  61  10  12 0.00
Wed 07/08 11Z 0.15 0209  59   8  12 0.00
Wed 07/08 12Z 0.17 0309  60   5  12 0.00
Wed 07/08 13Z 0.12 0307  61   4  12 0.00
Wed 07/08 14Z 0.06 0006  65   4  12 0.00
Wed 07/08 15Z 0.07 3406  67   6  13 0.00
Wed 07/08 16Z 0.10 3405  67   4  13 0.00
Wed 07/08 17Z 0.50 3104  69   3  13 0.00
Wed 07/08 18Z 0.73 3006  68   2  13 0.00
Wed 07/08 19Z 0.62 3007  64   3  14 0.00
Wed 07/08 20Z 0.59 3009  62   5  14 0.00
Wed 07/08 21Z 0.57 2911  69   6  14 0.00
Wed 07/08 22Z 0.55 2912  80   5  14 0.00
Wed 07/08 23Z 0.54 2812  85   9  14 0.00

Run total areal avg QPF for the greens is: 0.12 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