NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260416_0000
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)
=== ===== === ==== ==== === === === ====
Thu 04/16 00Z 0.67 2415  78  63  11 0.00
Thu 04/16 01Z 0.66 2515  78  63  11 0.00
Thu 04/16 02Z 0.57 2615  77  74  11 0.00
Thu 04/16 03Z 0.33 2610  73  88  12 0.00
Thu 04/16 04Z 0.31 2609  75  97  12 0.00
Thu 04/16 05Z 0.34 2610  89  94  10 0.07
Thu 04/16 06Z 0.25 2509  91  94  11 0.11
Thu 04/16 07Z 0.26 2410  91  94  11 0.03
Thu 04/16 08Z 0.21 2308  87  92  11 0.01
Thu 04/16 09Z 0.22 2309  89  93  11 0.00
Thu 04/16 10Z 0.29 2411  96  96  10 0.03
Thu 04/16 11Z 0.31 2511  98  94  10 0.04
Thu 04/16 12Z 0.24 2508  97  81  10 0.01
Thu 04/16 13Z 0.23 2408  97  74  10 0.00
Thu 04/16 14Z 0.26 2509  96  66  11 0.01
Thu 04/16 15Z 0.24 2509  94  53  11 0.00
Thu 04/16 16Z 0.24 2309  91  50  12 0.00
Thu 04/16 17Z 0.33 2312  91  60  12 0.00
Thu 04/16 18Z 0.37 2313  87  65  12 0.00
Thu 04/16 19Z 0.44 2313  83  69  13 0.00
Thu 04/16 20Z 0.50 2315  81  80  13 0.00
Thu 04/16 21Z 0.63 2317  84  54  13 0.00
Thu 04/16 22Z 0.63 2317  88  37  13 0.00
Thu 04/16 23Z 0.60 2217  92  83  12 0.02
Fri 04/17 00Z 0.58 2218  96  88  13 0.14
Fri 04/17 01Z 0.94 2522  94  80  12 0.18
Fri 04/17 02Z 0.77 2623  88  86  12 0.25
Fri 04/17 03Z 0.87 2624  89  72  11 0.00
Fri 04/17 04Z 0.92 2626  90  74  11 0.00
Fri 04/17 05Z 0.80 2725  91  75  11 0.00
Fri 04/17 06Z 0.63 2821  91  86  10 0.00
Fri 04/17 07Z 0.57 2820  96  83  10 0.02
Fri 04/17 08Z 0.46 2917  94  73   9 0.02
Fri 04/17 09Z 0.36 3015  96  71   9 0.02
Fri 04/17 10Z 0.31 3115  96  67   9 0.01
Fri 04/17 11Z 0.20 3215  96  71   9 0.01
Fri 04/17 12Z 0.12 3314  97  76   8 0.01
Fri 04/17 13Z 0.08 3315  97  83   8 0.00
Fri 04/17 14Z 0.05 3416  96  89   8 0.00
Fri 04/17 15Z 0.07 3516  95  83   7 0.00
Fri 04/17 16Z 0.11 0014  94  69   7 0.00
Fri 04/17 17Z 0.13 0012  94  50   7 0.00
Fri 04/17 18Z 0.13 0011  94  31   7 0.00
Fri 04/17 19Z 0.11 0010  92  21   7 0.00
Fri 04/17 20Z 0.09 0010  89  18   7 0.00
Fri 04/17 21Z 0.10 0010  86  18   8 0.00
Fri 04/17 22Z 0.15 0110  80  16   8 0.00
Fri 04/17 23Z 0.17 0210  73  15   9 0.00
Sat 04/18 00Z 0.19 0310  70  14   9 0.00
Sat 04/18 01Z 0.19 0509  69  16   9 0.00
Sat 04/18 02Z 0.19 0708  72  15   9 0.00
Sat 04/18 03Z 0.17 0907  78  14   9 0.00
Sat 04/18 04Z 0.15 1108  82  14   8 0.00
Sat 04/18 05Z 0.15 1309  88  13   8 0.00
Sat 04/18 06Z 0.17 1311  91  12   8 0.00
Sat 04/18 07Z 0.22 1315  92  12   8 0.00
Sat 04/18 08Z 0.19 1416  95  14   7 0.01
Sat 04/18 09Z 0.08 1617  97  14   7 0.01
Sat 04/18 10Z 0.10 1716  99  14   6 0.02
Sat 04/18 11Z 0.07 1716  98  11   6 0.01

Run total areal avg QPF for the Central_Greens is: 1.04 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