Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260628_0000
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)
=== ===== === ==== ==== === === === ====
Sun 06/28 00Z 0.07 3405  82  59  12 0.00
Sun 06/28 01Z 0.06 3406  80  58  12 0.00
Sun 06/28 02Z 0.03 0006  77  59  12 0.00
Sun 06/28 03Z 0.06 0106  74  59  12 0.00
Sun 06/28 04Z 0.09 0106  73  62  12 0.00
Sun 06/28 05Z 0.08 0106  73  66  11 0.00
Sun 06/28 06Z 0.04 0006  72  68  11 0.00
Sun 06/28 07Z 0.06 0006  71  56  12 0.00
Sun 06/28 08Z 0.06 0007  69  44  12 0.00
Sun 06/28 09Z 0.06 0008  68  38  11 0.00
Sun 06/28 10Z 0.06 0009  69  33  11 0.00
Sun 06/28 11Z 0.08 0010  70  29  11 0.00
Sun 06/28 12Z 0.11 0010  72  27  11 0.00
Sun 06/28 13Z 0.15 0109  76  28  11 0.00
Sun 06/28 14Z 0.20 0007  80  30  11 0.00
Sun 06/28 15Z 0.45 0005  82  31  11 0.00
Sun 06/28 16Z 0.65 3505  81  36  11 0.01
Sun 06/28 17Z 0.44 3504  78  41  12 0.03
Sun 06/28 18Z 0.38 3404  75  37  12 0.02
Sun 06/28 19Z 0.67 3304  74  32  12 0.01
Sun 06/28 20Z 0.94 3205  73  26  12 0.01
Sun 06/28 21Z 0.75 3307  72  21  12 0.00
Sun 06/28 22Z 0.44 3308  68  25  13 0.00
Sun 06/28 23Z 0.20 3308  61  22  13 0.00
Mon 06/29 00Z 0.11 3409  56  22  13 0.00
Mon 06/29 01Z 0.05 3509  56  21  13 0.00
Mon 06/29 02Z 0.06 0008  58  21  13 0.00
Mon 06/29 03Z 0.09 0008  59  22  12 0.00
Mon 06/29 04Z 0.11 3508  59  25  12 0.00
Mon 06/29 05Z 0.12 3507  60  25  12 0.00
Mon 06/29 06Z 0.17 0007  62  21  12 0.00
Mon 06/29 07Z 0.19 3507  63  19  12 0.00
Mon 06/29 08Z 0.18 3507  64  16  12 0.00
Mon 06/29 09Z 0.16 3407  65  13  12 0.00
Mon 06/29 10Z 0.16 3408  67  13  11 0.00
Mon 06/29 11Z 0.13 3508  68  10  11 0.00
Mon 06/29 12Z 0.14 3408  68  12  11 0.00
Mon 06/29 13Z 0.17 3406  70  12  11 0.00
Mon 06/29 14Z 0.28 3405  71  11  11 0.00
Mon 06/29 15Z 0.42 3304  71  10  12 0.00
Mon 06/29 16Z 0.76 3204  72  14  12 0.00
Mon 06/29 17Z 1.21 3104  71  16  12 0.00
Mon 06/29 18Z 1.37 3104  69  13  12 0.00
Mon 06/29 19Z 1.31 3004  65  10  13 0.00
Mon 06/29 20Z 1.36 3004  62   9  13 0.00
Mon 06/29 21Z 1.09 3005  59   8  13 0.00
Mon 06/29 22Z 0.53 2905  58   8  13 0.00
Mon 06/29 23Z 0.30 2904  61   9  13 0.00
Tue 06/30 00Z 0.29 2804  63   9  13 0.00
Tue 06/30 01Z 0.33 2704  66  12  13 0.00
Tue 06/30 02Z 0.39 2605  68  17  13 0.00
Tue 06/30 03Z 0.49 2607  70  20  13 0.00
Tue 06/30 04Z 0.58 2608  72  22  13 0.00
Tue 06/30 05Z 0.64 2609  74  22  13 0.00
Tue 06/30 06Z 0.66 2609  74  21  13 0.00
Tue 06/30 07Z 0.69 2610  76  17  13 0.00
Tue 06/30 08Z 0.69 2611  75  19  12 0.00
Tue 06/30 09Z 0.60 2610  74  25  12 0.00
Tue 06/30 10Z 0.54 2609  73  29  13 0.00
Tue 06/30 11Z 0.58 2610  74  33  13 0.00

Run total areal avg QPF for the greens is: 0.08 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