NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260511_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 05/11 06Z 0.55 3015  74  69   0 0.00
Mon 05/11 07Z 0.56 2916  76  64  -1 0.00
Mon 05/11 08Z 0.52 3016  80  31  -1 0.00
Mon 05/11 09Z 0.41 3116  79  25  -1 0.00
Mon 05/11 10Z 0.39 3117  73  28  -1 0.00
Mon 05/11 11Z 0.43 3117  71  31  -2 0.00
Mon 05/11 12Z 0.48 3016  67  36  -2 0.00
Mon 05/11 13Z 0.62 3013  62  40  -2 0.00
Mon 05/11 14Z 3.04 3012  60  58  -2 0.00
Mon 05/11 15Z 4.43 3011  59  65  -1 0.00
Mon 05/11 16Z 5.55 3010  63  80  -1 0.00
Mon 05/11 17Z 5.82 2810  75  85  -1 0.00
Mon 05/11 18Z 5.26 2811  76  77  -1 0.00
Mon 05/11 19Z 5.91 2811  72  70   0 0.00
Mon 05/11 20Z 4.66 2910  74  70  -1 0.00
Mon 05/11 21Z 2.33 3010  73  60  -1 0.01
Mon 05/11 22Z 1.87 3109  71  60  -1 0.00
Mon 05/11 23Z 0.75 3210  70  70  -1 0.00
Tue 05/12 00Z 0.23 3312  69  66  -1 0.00
Tue 05/12 01Z 0.19 3415  68  73  -2 0.00
Tue 05/12 02Z 0.17 3417  69  73  -2 0.00
Tue 05/12 03Z 0.25 3418  72  66  -2 0.00
Tue 05/12 04Z 0.24 3418  76  60  -3 0.00
Tue 05/12 05Z 0.24 3419  75  57  -3 0.00
Tue 05/12 06Z 0.18 3419  71  38  -3 0.00
Tue 05/12 07Z 0.08 3419  69  22  -3 0.00
Tue 05/12 08Z 0.05 3417  67  21  -3 0.00
Tue 05/12 09Z 0.04 3515  65  24  -4 0.00
Tue 05/12 10Z 0.08 3414  65  29  -4 0.00
Tue 05/12 11Z 0.16 3414  65  36  -4 0.00
Tue 05/12 12Z 0.90 3313  66  39  -4 0.00
Tue 05/12 13Z 2.24 3212  67  37  -4 0.00
Tue 05/12 14Z 3.20 3212  67  27  -4 0.00
Tue 05/12 15Z 3.63 3112  63  25  -4 0.00
Tue 05/12 16Z 4.71 3112  62  30  -3 0.00
Tue 05/12 17Z 6.33 3012  66  36  -3 0.00
Tue 05/12 18Z 5.82 3011  67  41  -2 0.00
Tue 05/12 19Z 5.70 2910  65  39  -1 0.00
Tue 05/12 20Z 4.51 3009  64  36  -1 0.00
Tue 05/12 21Z 3.86 3008  62  35   0 0.00
Tue 05/12 22Z 2.50 3007  61  33   0 0.00
Tue 05/12 23Z 0.89 2907  61  32   0 0.00
Wed 05/13 00Z 0.47 2806  60  31   0 0.00
Wed 05/13 01Z 0.40 2606  59  30   0 0.00
Wed 05/13 02Z 0.35 2305  59  28   0 0.00
Wed 05/13 03Z 0.37 2207  61  20   0 0.00
Wed 05/13 04Z 0.45 2209  63  12   0 0.00
Wed 05/13 05Z 0.51 2310  64   9   0 0.00
Wed 05/13 06Z 0.54 2211  65   9   0 0.00
Wed 05/13 07Z 0.52 2211  66  34   0 0.00
Wed 05/13 08Z 0.47 2112  69  71   0 0.00
Wed 05/13 09Z 0.42 2111  72  88   0 0.00
Wed 05/13 10Z 0.37 2012  75  96   0 0.00
Wed 05/13 11Z 0.20 1812  81  98   0 0.01
Wed 05/13 12Z 0.06 1715  86  98   0 0.01
Wed 05/13 13Z 0.05 1619  89  98   1 0.01
Wed 05/13 14Z 0.05 1722  92  97   1 0.01
Wed 05/13 15Z 0.07 1725  96  97   2 0.02
Wed 05/13 16Z 0.11 1724  96  98   3 0.04
Wed 05/13 17Z 0.05 1724  96  97   4 0.04

Run total areal avg QPF for the Central_Greens is: 0.15 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