NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261103_0000
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 00Z 0.71 2618  54  81   9 0.00
Tue 11/03 01Z 0.75 2619  54  79   9 0.00
Tue 11/03 02Z 0.75 2720  56  82   9 0.00
Tue 11/03 03Z 0.70 2720  56  86   9 0.00
Tue 11/03 04Z 0.66 2718  57  88   9 0.00
Tue 11/03 05Z 0.65 2717  59  89   9 0.00
Tue 11/03 06Z 0.61 2716  61  87   9 0.00
Tue 11/03 07Z 0.52 2715  61  87   9 0.00
Tue 11/03 08Z 0.45 2713  59  87   9 0.00
Tue 11/03 09Z 0.43 2712  58  88   9 0.00
Tue 11/03 10Z 0.40 2711  59  89   9 0.00
Tue 11/03 11Z 0.36 2610  59  86   9 0.00
Tue 11/03 12Z 0.31 2509  60  86   9 0.00
Tue 11/03 13Z 0.30 2410  63  92   9 0.00
Tue 11/03 14Z 0.26 2309  64  97   9 0.00
Tue 11/03 15Z 0.23 2110  62  98   9 0.00
Tue 11/03 16Z 0.27 2113  59  97   9 0.00
Tue 11/03 17Z 0.33 2115  57  93   9 0.00
Tue 11/03 18Z 0.40 2117  59  95   8 0.00
Tue 11/03 19Z 0.46 2219  66  93   8 0.00
Tue 11/03 20Z 0.52 2221  75  92   8 0.00
Tue 11/03 21Z 0.54 2222  91  86   9 0.01
Tue 11/03 22Z 0.53 2322  95  81   9 0.03
Tue 11/03 23Z 0.52 2421  96  78   9 0.03
Wed 11/04 00Z 0.51 2520  95  76  10 0.03
Wed 11/04 01Z 0.53 2521  96  83  10 0.02
Wed 11/04 02Z 0.58 2522  96  75  10 0.03
Wed 11/04 03Z 0.65 2623  95  75  10 0.01
Wed 11/04 04Z 0.68 2623  93  66  11 0.01
Wed 11/04 05Z 0.73 2624  87  63  11 0.00
Wed 11/04 06Z 0.72 2525  86  61  11 0.00
Wed 11/04 07Z 0.74 2526  82  55  11 0.00
Wed 11/04 08Z 0.76 2528  79  61  11 0.00
Wed 11/04 09Z 0.77 2429  77  66  11 0.00
Wed 11/04 10Z 0.80 2530  75  69  11 0.00
Wed 11/04 11Z 0.78 2529  71  68  11 0.00
Wed 11/04 12Z 0.75 2528  69  68  12 0.00
Wed 11/04 13Z 0.69 2526  68  63  12 0.00
Wed 11/04 14Z 0.64 2625  68  55  12 0.00
Wed 11/04 15Z 0.60 2622  71  47  12 0.00
Wed 11/04 16Z 0.60 2621  69  47  12 0.00
Wed 11/04 17Z 0.58 2619  70  47  12 0.00
Wed 11/04 18Z 0.53 2616  69  47  12 0.00
Wed 11/04 19Z 0.49 2615  68  51  12 0.00
Wed 11/04 20Z 0.44 2614  68  53  12 0.00
Wed 11/04 21Z 0.39 2513  67  54  13 0.00
Wed 11/04 22Z 0.35 2512  66  62  13 0.00
Wed 11/04 23Z 0.32 2512  66  64  13 0.00
Thu 11/05 00Z 0.34 2513  66  72  13 0.00
Thu 11/05 01Z 0.34 2414  65  78  13 0.00
Thu 11/05 02Z 0.32 2414  63  83  14 0.00
Thu 11/05 03Z 0.28 2313  61  83  14 0.00
Thu 11/05 04Z 0.27 2314  60  80  14 0.00
Thu 11/05 05Z 0.28 2216  58  81  15 0.00
Thu 11/05 06Z 0.29 2217  54  70  15 0.00
Thu 11/05 07Z 0.31 2219  50  65  15 0.00
Thu 11/05 08Z 0.33 2222  48  61  15 0.00
Thu 11/05 09Z 0.36 2224  49  53  15 0.00
Thu 11/05 10Z 0.39 2226  50  49  15 0.00
Thu 11/05 11Z 0.45 2328  54  49  15 0.00

Run total areal avg QPF for the greens is: 0.17 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