NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260503_1800
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)
=== ===== === ==== ==== === === === ====
Sun 05/03 18Z 6.25 3113  74  68  -3 0.00
Sun 05/03 19Z 6.80 3014  72  66  -2 0.00
Sun 05/03 20Z 7.02 2915  74  79  -2 0.00
Sun 05/03 21Z 5.13 2917  69  73  -2 0.00
Sun 05/03 22Z 5.90 2918  60  48  -1 0.00
Sun 05/03 23Z 3.60 2919  57  26  -1 0.00
Mon 05/04 00Z 1.74 2921  56  13  -1 0.00
Mon 05/04 01Z 1.67 2824  53   8  -1 0.00
Mon 05/04 02Z 1.13 2927  49   5  -1 0.00
Mon 05/04 03Z 1.01 2827  58  19   0 0.00
Mon 05/04 04Z 0.97 2727  70  66   0 0.00
Mon 05/04 05Z 0.84 2628  87  91   0 0.02
Mon 05/04 06Z 0.88 2632  91  92   0 0.04
Mon 05/04 07Z 0.86 2631  94  91   0 0.04
Mon 05/04 08Z 0.86 2630  94  84   0 0.02
Mon 05/04 09Z 0.90 2630  95  77   0 0.02
Mon 05/04 10Z 0.86 2630  92  71   1 0.02
Mon 05/04 11Z 0.88 2632  88  74   2 0.01
Mon 05/04 12Z 0.94 2633  79  84   2 0.00
Mon 05/04 13Z 1.07 2533  80  85   2 0.00
Mon 05/04 14Z 1.15 2531  81  83   2 0.00
Mon 05/04 15Z 1.57 2529  83  79   2 0.00
Mon 05/04 16Z 7.51 2527  82  78   2 0.01
Mon 05/04 17Z 13.22 2425  78  85   3 0.00
Mon 05/04 18Z 13.32 2424  76  81   4 0.00
Mon 05/04 19Z 14.28 2423  76  70   4 0.00
Mon 05/04 20Z 14.29 2421  73  59   5 0.00
Mon 05/04 21Z 11.48 2420  72  55   5 0.00
Mon 05/04 22Z 6.67 2322  73  51   6 0.00
Mon 05/04 23Z 1.58 2423  70  37   6 0.00
Tue 05/05 00Z 1.34 2324  72  26   6 0.00
Tue 05/05 01Z 1.35 2326  73  47   6 0.00
Tue 05/05 02Z 1.40 2327  74  19   6 0.00
Tue 05/05 03Z 1.43 2329  77  15   6 0.00
Tue 05/05 04Z 1.47 2332  79  10   5 0.00
Tue 05/05 05Z 1.35 2333  80   9   6 0.00
Tue 05/05 06Z 1.09 2332  76   9   6 0.00
Tue 05/05 07Z 0.96 2332  71   9   7 0.00
Tue 05/05 08Z 0.90 2333  70  10   7 0.00
Tue 05/05 09Z 0.85 2332  66   8   8 0.00
Tue 05/05 10Z 0.75 2231  74  14   8 0.00
Tue 05/05 11Z 0.76 2232  89  77   8 0.01
Tue 05/05 12Z 0.78 2235  90  66   8 0.00
Tue 05/05 13Z 0.86 2335  83  73   9 0.00
Tue 05/05 14Z 1.12 2334  82  73   9 0.00
Tue 05/05 15Z 1.17 2230  78  62  10 0.00
Tue 05/05 16Z 8.23 2227  79  47   9 0.00
Tue 05/05 17Z 10.20 2227  75  64  10 0.00
Tue 05/05 18Z 14.86 2129  71  64  11 0.00
Tue 05/05 19Z 10.70 2128  72  61  11 0.00
Tue 05/05 20Z 11.76 2030  72  63  11 0.00
Tue 05/05 21Z 6.51 2232  81  74  11 0.19
Tue 05/05 22Z 3.40 2132  82  78  11 0.03
Tue 05/05 23Z 1.34 2134  79  52  11 0.02
Wed 05/06 00Z 1.23 2036  71  36  11 0.00
Wed 05/06 01Z 1.32 2138  72  66  11 0.05
Wed 05/06 02Z 1.21 2331  82  59  10 0.12
Wed 05/06 03Z 0.97 2427  86  78   9 0.03
Wed 05/06 04Z 0.83 2423  91  90   9 0.12
Wed 05/06 05Z 0.65 2323  94  83   8 0.07

Run total areal avg QPF for the Central_Greens is: 0.82 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