NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260603_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)
=== ===== === ==== ==== === === === ====
Wed 06/03 00Z 0.34 3416  46  35   8 0.00
Wed 06/03 01Z 0.44 3318  43  38   8 0.00
Wed 06/03 02Z 0.39 3418  43  37   9 0.00
Wed 06/03 03Z 0.21 3417  43  37   9 0.00
Wed 06/03 04Z 0.09 3514  43  35   9 0.00
Wed 06/03 05Z 0.07 3513  43  29   9 0.00
Wed 06/03 06Z 0.06 3512  42  22   9 0.00
Wed 06/03 07Z 0.07 3511  42  17   9 0.00
Wed 06/03 08Z 0.07 3510  42  15   9 0.00
Wed 06/03 09Z 0.09 3509  42  13   9 0.00
Wed 06/03 10Z 0.12 3409  42  15   9 0.00
Wed 06/03 11Z 0.12 3407  42  19  10 0.00
Wed 06/03 12Z 0.27 3209  42  23  10 0.00
Wed 06/03 13Z 0.32 3211  42  28  10 0.00
Wed 06/03 14Z 0.39 3211  42  33  10 0.00
Wed 06/03 15Z 0.79 3111  43  37  10 0.00
Wed 06/03 16Z 1.73 3112  44  38  10 0.00
Wed 06/03 17Z 2.53 3112  45  40  10 0.00
Wed 06/03 18Z 3.17 3111  45  41  11 0.00
Wed 06/03 19Z 3.11 3111  47  42  11 0.00
Wed 06/03 20Z 2.33 3109  50  42  11 0.00
Wed 06/03 21Z 1.90 3009  52  44  11 0.00
Wed 06/03 22Z 0.98 2909  53  47  12 0.00
Wed 06/03 23Z 0.65 2809  54  49  12 0.00
Thu 06/04 00Z 0.73 2711  57  50  12 0.00
Thu 06/04 01Z 0.80 2713  59  48  12 0.00
Thu 06/04 02Z 0.87 2814  58  48  12 0.00
Thu 06/04 03Z 0.84 3015  56  46  11 0.00
Thu 06/04 04Z 0.59 3114  57  44  11 0.00
Thu 06/04 05Z 0.46 3013  56  42  12 0.00
Thu 06/04 06Z 0.41 3010  53  37  12 0.00
Thu 06/04 07Z 0.41 2910  51  33  12 0.00
Thu 06/04 08Z 0.46 2810  50  31  12 0.00
Thu 06/04 09Z 0.53 2811  49  29  12 0.00
Thu 06/04 10Z 0.55 2811  48  27  12 0.00
Thu 06/04 11Z 0.55 2811  48  27  12 0.00
Thu 06/04 12Z 0.64 2813  49  29  11 0.00
Thu 06/04 13Z 0.61 2813  52  31  11 0.00
Thu 06/04 14Z 0.77 2812  53  30  11 0.00
Thu 06/04 15Z 0.84 2711  54  31  11 0.00
Thu 06/04 16Z 1.53 2611  53  30  12 0.00
Thu 06/04 17Z 2.11 2611  50  27  12 0.00
Thu 06/04 18Z 2.77 2612  50  25  12 0.00
Thu 06/04 19Z 6.04 2613  57  26  12 0.00
Thu 06/04 20Z 7.26 2614  55  28  13 0.00
Thu 06/04 21Z 5.11 2614  53  26  13 0.00
Thu 06/04 22Z 3.18 2715  57  24  13 0.00
Thu 06/04 23Z 1.62 2716  55  23  13 0.00
Fri 06/05 00Z 1.65 2718  56  20  12 0.00
Fri 06/05 01Z 1.69 2820  61  20  12 0.00
Fri 06/05 02Z 1.18 2822  61  16  12 0.00
Fri 06/05 03Z 1.19 2923  68  12  11 0.00
Fri 06/05 04Z 1.01 2923  70  10  11 0.00
Fri 06/05 05Z 1.02 2924  71   9  11 0.00
Fri 06/05 06Z 0.99 3025  69  10  11 0.00
Fri 06/05 07Z 0.88 3024  65  12  11 0.00
Fri 06/05 08Z 0.81 3022  64  13  11 0.00
Fri 06/05 09Z 0.77 3022  64   9  10 0.00
Fri 06/05 10Z 0.73 3021  63   5  10 0.00
Fri 06/05 11Z 0.76 3021  62   6  10 0.00

Run total areal avg QPF for the greens is: 0.00 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