NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260929_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)
=== ===== === ==== ==== === === === ====
Tue 09/29 12Z 0.03 3411  95  88   9 0.00
Tue 09/29 13Z 0.05 3413  95  88   9 0.00
Tue 09/29 14Z 0.05 3413  94  88   8 0.00
Tue 09/29 15Z 0.03 3412  93  85   8 0.00
Tue 09/29 16Z 0.03 3411  93  80   8 0.00
Tue 09/29 17Z 0.03 3409  93  74   8 0.00
Tue 09/29 18Z 0.04 3408  92  69   9 0.00
Tue 09/29 19Z 0.05 3309  92  64   9 0.00
Tue 09/29 20Z 0.05 3408  92  67   9 0.00
Tue 09/29 21Z 0.03 3407  92  68   9 0.00
Tue 09/29 22Z 0.03 3408  93  66   9 0.00
Tue 09/29 23Z 0.03 3508  94  64   8 0.00
Wed 09/30 00Z 0.04 3508  93  61   8 0.00
Wed 09/30 01Z 0.04 0007  93  56   8 0.00
Wed 09/30 02Z 0.04 0006  94  51   8 0.00
Wed 09/30 03Z 0.04 0104  93  46   9 0.00
Wed 09/30 04Z 0.02 0003  92  45   9 0.00
Wed 09/30 05Z 0.03 3203  90  40   9 0.00
Wed 09/30 06Z 0.05 3003  90  32   9 0.00
Wed 09/30 07Z 0.02 3202  87  24  10 0.00
Wed 09/30 08Z 0.04 3002  86  19  10 0.00
Wed 09/30 09Z 0.07 3105  85  17  11 0.00
Wed 09/30 10Z 0.07 3005  82  17  11 0.00
Wed 09/30 11Z 0.08 3005  80  16  11 0.00
Wed 09/30 12Z 0.07 3005  78  14  11 0.00
Wed 09/30 13Z 0.05 3004  73  18  12 0.00
Wed 09/30 14Z 0.07 2803  72  24  12 0.00
Wed 09/30 15Z 0.08 2804  72  27  12 0.00
Wed 09/30 16Z 0.09 2804  71  28  12 0.00
Wed 09/30 17Z 0.11 2605  70  28  12 0.00
Wed 09/30 18Z 0.13 2606  68  23  12 0.00
Wed 09/30 19Z 0.15 2606  64  24  12 0.00
Wed 09/30 20Z 0.16 2606  57  25  13 0.00
Wed 09/30 21Z 0.20 2608  50  21  13 0.00
Wed 09/30 22Z 0.23 2609  42  14  13 0.00
Wed 09/30 23Z 0.27 2711  46  15  12 0.00
Thu 10/01 00Z 0.27 2711  56  29  12 0.00
Thu 10/01 01Z 0.28 2712  54  61  13 0.00
Thu 10/01 02Z 0.32 2814  56  63  13 0.00
Thu 10/01 03Z 0.33 2814  64  51  12 0.00
Thu 10/01 04Z 0.34 2815  69  50  12 0.00
Thu 10/01 05Z 0.32 2813  68  73  12 0.00
Thu 10/01 06Z 0.33 2813  72  73  12 0.00
Thu 10/01 07Z 0.41 2715  77  90  11 0.00
Thu 10/01 08Z 0.43 2515  79  87  11 0.00
Thu 10/01 09Z 0.49 2516  83  93  11 0.01
Thu 10/01 10Z 0.52 2617  79  92  11 0.00
Thu 10/01 11Z 0.49 2616  86  95  11 0.00
Thu 10/01 12Z 0.39 2815  84  93  12 0.00
Thu 10/01 13Z 0.37 2614  76  85  12 0.00
Thu 10/01 14Z 0.36 2414  74  72  13 0.00
Thu 10/01 15Z 0.39 2316  73  63  13 0.00
Thu 10/01 16Z 0.38 2217  63  65  13 0.00
Thu 10/01 17Z 0.44 2218  53  55  13 0.00
Thu 10/01 18Z 0.57 2319  62  63  13 0.00
Thu 10/01 19Z 0.93 2321  87  89  11 0.00
Thu 10/01 20Z 0.79 2323  95  96  11 0.01
Thu 10/01 21Z 0.76 2424  97  96  12 0.03
Thu 10/01 22Z 0.72 2424  97  94  12 0.02
Thu 10/01 23Z 0.76 2526  97  94  12 0.03

Run total areal avg QPF for the Central_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