NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260511_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 05/11 06Z 0.60 3015  76  66  -1 0.00
Mon 05/11 07Z 0.60 2915  80  58  -1 0.00
Mon 05/11 08Z 0.59 2916  84  36  -1 0.00
Mon 05/11 09Z 0.56 3016  82  31  -2 0.00
Mon 05/11 10Z 0.55 3017  77  34  -2 0.00
Mon 05/11 11Z 0.58 3017  75  36  -2 0.00
Mon 05/11 12Z 0.60 3016  73  40  -2 0.00
Mon 05/11 13Z 0.71 3014  70  42  -2 0.00
Mon 05/11 14Z 2.86 3012  69  57  -2 0.00
Mon 05/11 15Z 4.38 3011  68  65  -2 0.00
Mon 05/11 16Z 5.21 2910  70  75  -2 0.00
Mon 05/11 17Z 5.02 2811  79  83  -1 0.00
Mon 05/11 18Z 4.77 2811  78  77  -1 0.01
Mon 05/11 19Z 4.98 2812  74  73  -1 0.01
Mon 05/11 20Z 4.07 2911  76  65  -1 0.00
Mon 05/11 21Z 3.01 3011  74  58  -1 0.01
Mon 05/11 22Z 2.68 3110  71  51  -1 0.00
Mon 05/11 23Z 1.78 3211  70  56  -1 0.00
Tue 05/12 00Z 1.36 3213  69  51  -2 0.00
Tue 05/12 01Z 0.94 3316  69  55  -2 0.00
Tue 05/12 02Z 0.72 3317  70  56  -2 0.00
Tue 05/12 03Z 0.64 3318  70  54  -2 0.00
Tue 05/12 04Z 0.62 3318  72  49  -3 0.00
Tue 05/12 05Z 0.45 3418  72  47  -3 0.00
Tue 05/12 06Z 0.32 3418  69  34  -3 0.00
Tue 05/12 07Z 0.21 3417  67  25  -3 0.00
Tue 05/12 08Z 0.16 3515  65  27  -4 0.00
Tue 05/12 09Z 0.15 3514  65  31  -4 0.00
Tue 05/12 10Z 0.25 3413  66  37  -4 0.00
Tue 05/12 11Z 0.36 3312  67  39  -4 0.00
Tue 05/12 12Z 1.12 3212  68  38  -5 0.00
Tue 05/12 13Z 2.97 3211  69  34  -5 0.00
Tue 05/12 14Z 4.50 3111  69  28  -4 0.00
Tue 05/12 15Z 4.94 3111  66  31  -4 0.00
Tue 05/12 16Z 5.95 3112  65  34  -3 0.00
Tue 05/12 17Z 7.17 3012  69  40  -3 0.00
Tue 05/12 18Z 6.23 3011  69  42  -2 0.00
Tue 05/12 19Z 6.11 3011  67  42  -2 0.00
Tue 05/12 20Z 5.02 3009  65  39  -1 0.00
Tue 05/12 21Z 4.10 3009  63  36  -1 0.00
Tue 05/12 22Z 2.44 3007  62  33   0 0.00
Tue 05/12 23Z 0.92 2907  62  32   0 0.00
Wed 05/13 00Z 0.46 2806  61  31   0 0.00
Wed 05/13 01Z 0.37 2706  60  30   0 0.00
Wed 05/13 02Z 0.30 2505  61  29   0 0.00
Wed 05/13 03Z 0.29 2306  63  24   0 0.00
Wed 05/13 04Z 0.35 2307  64  19   0 0.00
Wed 05/13 05Z 0.39 2309  64  16   0 0.00
Wed 05/13 06Z 0.38 2209  64  14   0 0.00
Wed 05/13 07Z 0.36 2210  65  27   0 0.00
Wed 05/13 08Z 0.32 2111  67  54   0 0.00
Wed 05/13 09Z 0.29 2011  69  76   0 0.00
Wed 05/13 10Z 0.20 1912  72  92   0 0.00
Wed 05/13 11Z 0.07 1813  78  96   0 0.00
Wed 05/13 12Z 0.07 1715  85  96   0 0.01
Wed 05/13 13Z 0.12 1619  88  97   0 0.01
Wed 05/13 14Z 0.14 1622  90  97   1 0.01
Wed 05/13 15Z 0.16 1625  93  97   2 0.02
Wed 05/13 16Z 0.15 1725  94  97   2 0.03
Wed 05/13 17Z 0.13 1626  95  96   3 0.03

Run total areal avg QPF for the greens is: 0.14 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