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_1200
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 12Z 0.29 3316  87  71  -5 0.00
Sun 05/03 13Z 1.43 3317  86  72  -4 0.00
Sun 05/03 14Z 3.69 3217  83  71  -4 0.00
Sun 05/03 15Z 4.90 3217  73  62  -4 0.00
Sun 05/03 16Z 6.15 3117  69  57  -3 0.00
Sun 05/03 17Z 5.64 3117  78  63  -3 0.00
Sun 05/03 18Z 6.32 3116  73  61  -3 0.00
Sun 05/03 19Z 7.60 3016  69  64  -2 0.00
Sun 05/03 20Z 8.88 2917  68  55  -2 0.00
Sun 05/03 21Z 9.95 2919  65  50  -2 0.00
Sun 05/03 22Z 8.66 2919  62  36  -1 0.00
Sun 05/03 23Z 4.18 2920  57  21  -1 0.00
Mon 05/04 00Z 2.02 2922  53   9  -1 0.00
Mon 05/04 01Z 1.63 2823  48   3  -1 0.00
Mon 05/04 02Z 1.01 2823  45   5   0 0.00
Mon 05/04 03Z 1.00 2724  60  23   0 0.00
Mon 05/04 04Z 1.14 2624  71  73   0 0.00
Mon 05/04 05Z 0.92 2624  83  91   0 0.00
Mon 05/04 06Z 0.72 2725  93  91   0 0.02
Mon 05/04 07Z 0.77 2727  95  93   0 0.02
Mon 05/04 08Z 0.73 2727  96  85   1 0.02
Mon 05/04 09Z 0.82 2629  97  89   1 0.03
Mon 05/04 10Z 0.90 2630  94  82   1 0.04
Mon 05/04 11Z 0.88 2630  88  79   1 0.01
Mon 05/04 12Z 0.96 2631  85  66   1 0.00
Mon 05/04 13Z 1.05 2530  83  67   1 0.00
Mon 05/04 14Z 1.23 2530  84  78   2 0.00
Mon 05/04 15Z 2.29 2429  89  79   1 0.00
Mon 05/04 16Z 1.38 2428  90  72   2 0.01
Mon 05/04 17Z 2.95 2426  89  69   2 0.00
Mon 05/04 18Z 4.65 2424  87  55   3 0.00
Mon 05/04 19Z 10.94 2422  85  42   3 0.00
Mon 05/04 20Z 11.87 2421  83  41   4 0.00
Mon 05/04 21Z 8.81 2421  82  30   4 0.00
Mon 05/04 22Z 5.12 2421  79  25   5 0.00
Mon 05/04 23Z 1.86 2322  78  26   5 0.00
Tue 05/05 00Z 1.63 2324  77  21   6 0.00
Tue 05/05 01Z 1.41 2326  79  16   6 0.00
Tue 05/05 02Z 1.25 2327  79  14   6 0.00
Tue 05/05 03Z 1.24 2330  80  11   6 0.00
Tue 05/05 04Z 1.24 2331  81  27   6 0.00
Tue 05/05 05Z 1.23 2333  83  12   6 0.00
Tue 05/05 06Z 1.14 2334  86   9   6 0.00
Tue 05/05 07Z 0.97 2332  86   4   7 0.01
Tue 05/05 08Z 0.79 2331  85   1   8 0.01
Tue 05/05 09Z 0.83 2333  89   7   8 0.01
Tue 05/05 10Z 0.90 2336  88  73   8 0.01
Tue 05/05 11Z 0.84 2434  88  87   9 0.01
Tue 05/05 12Z 0.87 2333  86  59   9 0.00
Tue 05/05 13Z 0.95 2333  85  68   9 0.00
Tue 05/05 14Z 1.13 2332  83  80   9 0.00
Tue 05/05 15Z 1.32 2328  78  81  10 0.00
Tue 05/05 16Z 6.38 2226  76  82  10 0.00
Tue 05/05 17Z 10.51 2225  75  85  10 0.00
Tue 05/05 18Z 12.15 2125  72  87  11 0.00
Tue 05/05 19Z 12.00 2125  73  76  11 0.00
Tue 05/05 20Z 10.05 2028  73  40  12 0.00
Tue 05/05 21Z 9.26 2031  72  28  12 0.00
Tue 05/05 22Z 5.25 2034  71  29  11 0.00
Tue 05/05 23Z 2.57 2134  69  52  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.20 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