NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260605_1200
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)
=== ===== === ==== ==== === === === ====
Fri 06/05 12Z 0.27 3010  59  10  13 0.00
Fri 06/05 13Z 0.28 2909  58  10  13 0.00
Fri 06/05 14Z 0.31 2908  57  11  13 0.00
Fri 06/05 15Z 0.38 2808  57  12  13 0.00
Fri 06/05 16Z 0.63 2807  56  13  13 0.00
Fri 06/05 17Z 1.38 2808  55  14  13 0.00
Fri 06/05 18Z 2.02 2808  53  16  13 0.00
Fri 06/05 19Z 2.99 2708  55  17  13 0.00
Fri 06/05 20Z 3.14 2708  58  17  13 0.00
Fri 06/05 21Z 2.36 2708  59  13  14 0.00
Fri 06/05 22Z 1.04 2608  60  11  14 0.00
Fri 06/05 23Z 0.65 2608  58   8  14 0.00
Sat 06/06 00Z 0.79 2610  55  13  14 0.00
Sat 06/06 01Z 0.80 2510  58  10  14 0.00
Sat 06/06 02Z 0.78 2510  60  13  14 0.00
Sat 06/06 03Z 0.94 2412  59  14  14 0.00
Sat 06/06 04Z 1.19 2415  60  22  14 0.00
Sat 06/06 05Z 1.30 2517  62  27  14 0.00
Sat 06/06 06Z 1.24 2518  65  28  13 0.00
Sat 06/06 07Z 1.11 2517  68  24  13 0.00
Sat 06/06 08Z 1.04 2417  72  41  13 0.00
Sat 06/06 09Z 0.85 2316  75  54  13 0.01
Sat 06/06 10Z 0.75 2217  77  64  12 0.00
Sat 06/06 11Z 0.68 2218  77  62  12 0.00
Sat 06/06 12Z 0.67 2119  76  50  13 0.00
Sat 06/06 13Z 0.84 2121  77  57  13 0.00
Sat 06/06 14Z 0.94 2121  79  79  12 0.00
Sat 06/06 15Z 1.17 2122  85  92  12 0.00
Sat 06/06 16Z 0.68 2124  90  97  12 0.02
Sat 06/06 17Z 0.65 2127  92  97  12 0.04
Sat 06/06 18Z 0.63 2128  88  92  13 0.04
Sat 06/06 19Z 0.68 2129  93  90  13 0.03
Sat 06/06 20Z 0.69 2230  95  83  14 0.06
Sat 06/06 21Z 0.81 2329  96  78  14 0.05
Sat 06/06 22Z 0.93 2426  96  73  14 0.01
Sat 06/06 23Z 0.88 2424  95  76  14 0.04
Sun 06/07 00Z 0.92 2424  95  78  14 0.03
Sun 06/07 01Z 0.88 2425  92  73  13 0.08
Sun 06/07 02Z 0.98 2428  95  76  13 0.03
Sun 06/07 03Z 1.09 2528  96  68  12 0.05
Sun 06/07 04Z 1.05 2628  98  78  11 0.04
Sun 06/07 05Z 0.97 2829  98  86  11 0.07
Sun 06/07 06Z 0.92 2929  98  92  10 0.09
Sun 06/07 07Z 0.99 3032  98  93  10 0.11
Sun 06/07 08Z 0.98 3032  98  79   9 0.08
Sun 06/07 09Z 1.05 3033  98  70   9 0.09
Sun 06/07 10Z 1.05 3034  98  68   8 0.09
Sun 06/07 11Z 0.92 3133  98  73   8 0.06
Sun 06/07 12Z 0.79 3131  97  75   7 0.04
Sun 06/07 13Z 0.70 3228  98  76   7 0.04
Sun 06/07 14Z 0.60 3226  98  75   7 0.04
Sun 06/07 15Z 0.48 3225  98  75   6 0.04
Sun 06/07 16Z 0.36 3325  98  71   6 0.03
Sun 06/07 17Z 0.27 3325  97  70   5 0.02
Sun 06/07 18Z 0.21 3425  95  65   5 0.01
Sun 06/07 19Z 0.19 3525  94  49   4 0.00
Sun 06/07 20Z 0.16 3525  94  27   4 0.01
Sun 06/07 21Z 0.18 3525  92  11   4 0.00
Sun 06/07 22Z 0.28 0026  90   3   4 0.00
Sun 06/07 23Z 0.26 0029  86   2   4 0.00

Run total areal avg QPF for the greens is: 1.35 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