NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261103_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)
=== ===== === ==== ==== === === === ====
Tue 11/03 06Z 0.46 2814  59  86   9 0.00
Tue 11/03 07Z 0.45 2814  58  86   9 0.00
Tue 11/03 08Z 0.41 2812  56  87   9 0.00
Tue 11/03 09Z 0.34 2710  56  83  10 0.00
Tue 11/03 10Z 0.33 2610  58  90   9 0.00
Tue 11/03 11Z 0.36 2610  61  92   9 0.00
Tue 11/03 12Z 0.36 2510  63  94   9 0.00
Tue 11/03 13Z 0.37 2411  63  91   9 0.00
Tue 11/03 14Z 0.36 2311  61  94   9 0.00
Tue 11/03 15Z 0.35 2212  61  94   9 0.00
Tue 11/03 16Z 0.40 2215  63  90   9 0.00
Tue 11/03 17Z 0.46 2217  66  90   8 0.00
Tue 11/03 18Z 0.48 2217  69  96   8 0.00
Tue 11/03 19Z 0.48 2218  75  98   8 0.00
Tue 11/03 20Z 0.51 2221  81  96   8 0.01
Tue 11/03 21Z 0.62 2224  85  93   8 0.00
Tue 11/03 22Z 0.62 2325  91  87   9 0.01
Tue 11/03 23Z 0.65 2425  92  80   9 0.02
Wed 11/04 00Z 0.65 2525  94  76  10 0.01
Wed 11/04 01Z 0.68 2625  93  64  10 0.01
Wed 11/04 02Z 0.69 2624  91  60  10 0.01
Wed 11/04 03Z 0.73 2725  89  57  10 0.01
Wed 11/04 04Z 0.75 2625  87  55  10 0.01
Wed 11/04 05Z 0.78 2625  83  51  10 0.00
Wed 11/04 06Z 0.82 2526  83  48  10 0.00
Wed 11/04 07Z 0.78 2526  79  44  10 0.00
Wed 11/04 08Z 0.76 2526  72  43  11 0.00
Wed 11/04 09Z 0.81 2527  70  62  11 0.00
Wed 11/04 10Z 0.81 2627  70  72  11 0.00
Wed 11/04 11Z 0.82 2627  70  66  11 0.00
Wed 11/04 12Z 0.83 2528  70  67  11 0.00
Wed 11/04 13Z 0.79 2527  69  74  11 0.00
Wed 11/04 14Z 0.72 2626  66  74  12 0.00
Wed 11/04 15Z 0.64 2624  64  68  12 0.00
Wed 11/04 16Z 0.57 2521  61  65  12 0.00
Wed 11/04 17Z 0.51 2519  58  64  13 0.00
Wed 11/04 18Z 0.48 2518  55  54  13 0.00
Wed 11/04 19Z 0.44 2417  54  44  13 0.00
Wed 11/04 20Z 0.43 2416  57  44  13 0.00
Wed 11/04 21Z 0.44 2417  59  46  13 0.00
Wed 11/04 22Z 0.45 2418  61  47  13 0.00
Wed 11/04 23Z 0.46 2418  63  42  13 0.00
Thu 11/05 00Z 0.45 2419  63  44  13 0.00
Thu 11/05 01Z 0.41 2418  61  46  13 0.00
Thu 11/05 02Z 0.39 2418  57  51  14 0.00
Thu 11/05 03Z 0.38 2319  52  60  14 0.00
Thu 11/05 04Z 0.40 2320  48  64  14 0.00
Thu 11/05 05Z 0.42 2322  41  65  14 0.00
Thu 11/05 06Z 0.43 2224  37  50  14 0.00
Thu 11/05 07Z 0.48 2227  37  41  14 0.00
Thu 11/05 08Z 0.50 2328  39  36  14 0.00
Thu 11/05 09Z 0.48 2228  41  37  14 0.00
Thu 11/05 10Z 0.46 2228  43  40  14 0.00
Thu 11/05 11Z 0.47 2230  44  42  14 0.00
Thu 11/05 12Z 0.52 2232  48  55  14 0.00
Thu 11/05 13Z 0.56 2233  53  65  14 0.00
Thu 11/05 14Z 0.52 2232  65  68  14 0.00
Thu 11/05 15Z 0.49 2230  72  76  13 0.00
Thu 11/05 16Z 0.50 2229  84  90  12 0.00
Thu 11/05 17Z 0.55 2229  96  92  11 0.01

Run total areal avg QPF for the greens is: 0.10 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