NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260605_1200
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)
=== ===== === ==== ==== === === === ====
Fri 06/05 12Z 0.27 3011  60   6  13 0.00
Fri 06/05 13Z 0.29 2910  59   7  13 0.00
Fri 06/05 14Z 0.34 2909  58   9  13 0.00
Fri 06/05 15Z 0.43 2909  57  10  13 0.00
Fri 06/05 16Z 0.76 2808  55  11  13 0.00
Fri 06/05 17Z 1.77 2908  53  12  13 0.00
Fri 06/05 18Z 2.51 2908  51  14  13 0.00
Fri 06/05 19Z 3.83 2808  54  14  13 0.00
Fri 06/05 20Z 4.07 2708  59  11  14 0.00
Fri 06/05 21Z 2.96 2708  60   8  14 0.00
Fri 06/05 22Z 1.12 2608  62   7  14 0.00
Fri 06/05 23Z 0.69 2609  59   8  14 0.00
Sat 06/06 00Z 0.86 2610  56  17  14 0.00
Sat 06/06 01Z 0.86 2610  59  11  14 0.00
Sat 06/06 02Z 0.84 2610  60  13  14 0.00
Sat 06/06 03Z 0.94 2512  61  16  14 0.00
Sat 06/06 04Z 1.11 2514  61  27  14 0.00
Sat 06/06 05Z 1.23 2516  63  27  14 0.00
Sat 06/06 06Z 1.10 2516  66  24  13 0.00
Sat 06/06 07Z 1.06 2515  70  24  13 0.00
Sat 06/06 08Z 0.86 2414  75  40  13 0.00
Sat 06/06 09Z 0.75 2314  77  51  13 0.01
Sat 06/06 10Z 0.76 2216  78  59  13 0.00
Sat 06/06 11Z 0.78 2218  76  53  13 0.00
Sat 06/06 12Z 0.84 2119  75  41  13 0.00
Sat 06/06 13Z 1.03 2120  75  47  13 0.00
Sat 06/06 14Z 1.05 2220  79  82  13 0.00
Sat 06/06 15Z 0.98 2222  87  96  12 0.01
Sat 06/06 16Z 0.78 2224  90  97  12 0.03
Sat 06/06 17Z 0.80 2126  93  96  12 0.04
Sat 06/06 18Z 0.81 2128  87  90  13 0.03
Sat 06/06 19Z 0.84 2129  94  87  13 0.03
Sat 06/06 20Z 0.81 2229  94  80  14 0.07
Sat 06/06 21Z 0.92 2328  96  75  14 0.06
Sat 06/06 22Z 1.05 2426  95  67  14 0.01
Sat 06/06 23Z 0.93 2425  94  76  14 0.04
Sun 06/07 00Z 0.94 2424  94  80  14 0.03
Sun 06/07 01Z 0.94 2425  92  67  14 0.10
Sun 06/07 02Z 1.10 2429  96  71  13 0.02
Sun 06/07 03Z 1.23 2530  97  65  12 0.03
Sun 06/07 04Z 1.09 2629  98  81  11 0.04
Sun 06/07 05Z 0.92 2829  98  89  11 0.05
Sun 06/07 06Z 0.87 2930  98  93  10 0.08
Sun 06/07 07Z 0.89 3032  98  93  10 0.10
Sun 06/07 08Z 0.87 3031  97  81   9 0.06
Sun 06/07 09Z 0.92 2931  98  59   9 0.04
Sun 06/07 10Z 0.90 3033  98  59   8 0.04
Sun 06/07 11Z 0.72 3132  97  67   8 0.03
Sun 06/07 12Z 0.65 3130  97  67   8 0.01
Sun 06/07 13Z 0.63 3127  98  67   8 0.01
Sun 06/07 14Z 0.57 3126  98  65   7 0.02
Sun 06/07 15Z 0.46 3225  98  66   7 0.04
Sun 06/07 16Z 0.33 3226  98  59   7 0.02
Sun 06/07 17Z 0.23 3326  96  58   6 0.01
Sun 06/07 18Z 0.14 3325  95  59   6 0.00
Sun 06/07 19Z 0.11 3425  94  56   5 0.00
Sun 06/07 20Z 0.16 3525  93  38   4 0.00
Sun 06/07 21Z 0.13 3524  91  15   4 0.00
Sun 06/07 22Z 0.29 3526  93   3   3 0.00
Sun 06/07 23Z 0.57 0029  87   3   4 0.00

Run total areal avg QPF for the Central_Greens is: 1.06 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