NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261102_1800
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)
=== ===== === ==== ==== === === === ====
Mon 11/02 18Z 0.66 2717  59  78   8 0.00
Mon 11/02 19Z 0.66 2718  60  79   8 0.00
Mon 11/02 20Z 0.71 2718  58  77   8 0.00
Mon 11/02 21Z 0.83 2620  55  78   8 0.00
Mon 11/02 22Z 0.82 2619  54  75   8 0.00
Mon 11/02 23Z 0.86 2620  53  75   8 0.00
Tue 11/03 00Z 0.84 2621  51  74   9 0.00
Tue 11/03 01Z 0.78 2620  50  77   9 0.00
Tue 11/03 02Z 0.74 2620  50  85   9 0.00
Tue 11/03 03Z 0.73 2720  52  88   9 0.00
Tue 11/03 04Z 0.70 2720  53  87   9 0.00
Tue 11/03 05Z 0.61 2717  51  80   9 0.00
Tue 11/03 06Z 0.60 2717  47  85   9 0.00
Tue 11/03 07Z 0.57 2716  45  88   9 0.00
Tue 11/03 08Z 0.53 2715  45  86   9 0.00
Tue 11/03 09Z 0.45 2713  44  89   9 0.00
Tue 11/03 10Z 0.41 2712  48  93   9 0.00
Tue 11/03 11Z 0.43 2612  54  95   9 0.00
Tue 11/03 12Z 0.45 2612  56  94   9 0.00
Tue 11/03 13Z 0.42 2511  56  93   8 0.00
Tue 11/03 14Z 0.38 2411  58  92   8 0.00
Tue 11/03 15Z 0.37 2311  62  93   8 0.00
Tue 11/03 16Z 0.36 2213  62  91   8 0.00
Tue 11/03 17Z 0.38 2215  61  92   8 0.00
Tue 11/03 18Z 0.48 2217  66  95   8 0.00
Tue 11/03 19Z 0.51 2219  79  93   8 0.00
Tue 11/03 20Z 0.52 2322  91  90   9 0.01
Tue 11/03 21Z 0.52 2322  94  86   9 0.01
Tue 11/03 22Z 0.60 2424  94  86  10 0.01
Tue 11/03 23Z 0.65 2426  94  84  10 0.02
Wed 11/04 00Z 0.67 2526  94  77  10 0.02
Wed 11/04 01Z 0.66 2526  95  70  11 0.01
Wed 11/04 02Z 0.69 2625  95  60  11 0.02
Wed 11/04 03Z 0.73 2626  94  54  11 0.01
Wed 11/04 04Z 0.75 2527  90  49  11 0.00
Wed 11/04 05Z 0.77 2528  82  40  11 0.00
Wed 11/04 06Z 0.81 2530  79  42  11 0.00
Wed 11/04 07Z 0.85 2531  77  39  11 0.00
Wed 11/04 08Z 0.89 2532  77  47  11 0.00
Wed 11/04 09Z 0.89 2531  75  54  11 0.00
Wed 11/04 10Z 0.90 2631  73  61  11 0.00
Wed 11/04 11Z 0.89 2630  73  58  11 0.00
Wed 11/04 12Z 0.89 2729  75  58  11 0.00
Wed 11/04 13Z 0.91 2728  75  56  11 0.00
Wed 11/04 14Z 0.91 2726  75  53  11 0.00
Wed 11/04 15Z 0.85 2725  74  53  11 0.00
Wed 11/04 16Z 0.74 2823  73  53  11 0.00
Wed 11/04 17Z 0.66 2821  73  54  12 0.00
Wed 11/04 18Z 0.63 2820  72  53  12 0.00
Wed 11/04 19Z 0.62 2819  71  51  12 0.00
Wed 11/04 20Z 0.58 2818  70  54  12 0.00
Wed 11/04 21Z 0.57 2718  69  57  12 0.00
Wed 11/04 22Z 0.56 2717  69  52  12 0.00
Wed 11/04 23Z 0.55 2717  69  46  12 0.00
Thu 11/05 00Z 0.52 2716  69  45  12 0.00
Thu 11/05 01Z 0.48 2714  68  43  12 0.00
Thu 11/05 02Z 0.41 2713  65  55  13 0.00
Thu 11/05 03Z 0.32 2610  63  56  13 0.00
Thu 11/05 04Z 0.25 2509  60  61  13 0.00

Run total areal avg QPF for the greens is: 0.11 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