Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260331_0000
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)
=== ===== === ==== ==== === === === ====
Tue 03/31 00Z 1.21 2523  60  93   6 0.00
Tue 03/31 01Z 1.60 2626  67  80   6 0.00
Tue 03/31 02Z 1.47 2729  72  63   6 0.00
Tue 03/31 03Z 1.46 2729  73  51   6 0.00
Tue 03/31 04Z 1.22 2727  80  52   5 0.00
Tue 03/31 05Z 0.91 2723  84  77   5 0.00
Tue 03/31 06Z 0.68 2719  88  89   5 0.03
Tue 03/31 07Z 0.54 2516  90  93   5 0.02
Tue 03/31 08Z 0.43 2415  95  88   6 0.03
Tue 03/31 09Z 0.44 2416  97  84   6 0.03
Tue 03/31 10Z 0.43 2316  97  86   6 0.02
Tue 03/31 11Z 0.44 2319  98  96   6 0.02
Tue 03/31 12Z 0.53 2224  98  93   7 0.09
Tue 03/31 13Z 0.64 2226  98  99   7 0.12
Tue 03/31 14Z 0.82 2332  98  95   7 0.06
Tue 03/31 15Z 0.91 2434  98  88   8 0.07
Tue 03/31 16Z 0.83 2530  97  84   8 0.06
Tue 03/31 17Z 0.83 2529  98  67   8 0.02
Tue 03/31 20Z 0.77 2426  99  85   9 0.02
Tue 03/31 21Z 0.80 2427  99  75   9 0.03
Tue 03/31 22Z 0.75 2327  99  73   9 0.04
Tue 03/31 23Z 0.70 2227  98  71  10 0.03
Wed 04/01 02Z 0.87 2236  98  94  10 0.03
Wed 04/01 03Z 1.03 2240  98  94  10 0.02
Wed 04/01 04Z 1.23 2341  98  91  10 0.06
Wed 04/01 05Z 1.38 2337  96  98   9 0.10
Wed 04/01 06Z 1.39 2439  99  80   9 0.08
Wed 04/01 07Z 1.28 2537  98  76   9 0.18
Wed 04/01 08Z 1.11 2537  98  78   9 0.15
Wed 04/01 09Z 0.89 2634  98  68   8 0.23
Wed 04/01 10Z 0.64 2730  98  81   8 0.10
Wed 04/01 11Z 0.43 2826  98  70   7 0.04
Wed 04/01 12Z 0.32 2923  95  55   6 0.03
Wed 04/01 13Z 0.27 3023  91  37   5 0.03
Wed 04/01 14Z 0.24 3123  86  13   3 0.03
Wed 04/01 15Z 0.21 3124  77   6   2 0.03
Wed 04/01 17Z 0.20 3223  72  12   0 0.02
Wed 04/01 18Z 0.16 3221  72  14   0 0.01
Wed 04/01 19Z 0.11 3319  71  16  -1 0.00
Wed 04/01 20Z 0.06 3417  70  17  -2 0.00
Wed 04/01 21Z 0.04 3513  67  21  -1 0.00
Wed 04/01 22Z 0.05 0011  66  22  -1 0.00
Wed 04/01 23Z 0.08 0108  64  24  -1 0.00
Thu 04/02 00Z 0.10 0307  62  26  -1 0.00
Thu 04/02 01Z 0.13 0507  53  30   0 0.00
Thu 04/02 02Z 0.11 0805  46  34   0 0.00
Thu 04/02 03Z 0.11 1107  44  36   0 0.00
Thu 04/02 04Z 0.11 1309  49  38   0 0.00
Thu 04/02 05Z 0.08 1512  55  40   0 0.00
Thu 04/02 06Z 0.07 1514  61  42   0 0.00
Thu 04/02 07Z 0.06 1516  65  60   0 0.00
Thu 04/02 08Z 0.05 1617  66  75   0 0.00
Thu 04/02 09Z 0.04 1616  68  78   1 0.00
Thu 04/02 10Z 0.04 1616  72  96   1 0.00
Thu 04/02 11Z 0.04 1615  79  98   1 0.00

Run total areal avg QPF for the Central_Greens is: 1.83 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