<div dir="ltr"><p class="MsoNormal" style="text-align:justify;line-height:12.65pt;background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial;margin:0in 0in 10pt;font-size:11pt;font-family:Calibri,sans-serif"><span style="font-size:12pt;font-family:"Times New Roman",serif"> </span><span style="font-family:"Times New Roman",serif;font-size:12pt">Dear NCL talk
colleagues</span></p>

<pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif">I’m interpolating wind, extracted from METAR, using  obj_anal_ic function. </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif">I take as first guess the wind at 10m (UGRD_P0_L103_GLL0 and VGRD_P0_L103_GLL0 variables) from GFS analysis at 2019-02-28:18Z (</span><span style="color:black"><a href="https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.2019022818/gfs.t18z.pgrb2.0p25.anl"><span style="color:blue">gfs.t18z.pgrb2.0p25.anl</span></a>)</span><span style="font-size:12pt;font-family:"Times New Roman",serif">and use a rscan=(/0.1,0.01/). </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif">The METAR information is also taken for this data and time. </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif"> </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif">Fig. </span><span style="font-family:"Times New Roman",serif">Vgfs_A20190228_1800png</span><span style="font-size:12pt;font-family:"Times New Roman",serif">  shows the GFS analysis wind and Fig. </span><span style="font-family:"Times New Roman",serif">CressmanInterpolation19-02-28_18Z</span><span style="font-size:12pt;font-family:"Times New Roman",serif">.png, the interpolated wind. </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="font-size:12pt;font-family:"Times New Roman",serif">These Figs, also contain wind barbs (plotted in black) at airports.  </span></pre><pre style="margin:0in 0in 0.0001pt;font-size:10pt;font-family:"Courier New""><span style="color:black"> </span></pre>

<p class="MsoNormal" style="text-align:justify;line-height:12.65pt;background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial;margin:0in 0in 10pt;font-size:11pt;font-family:Calibri,sans-serif"><span style="font-size:12pt;font-family:"Times New Roman",serif">Comparing these two
Figs., it can be seen that, in some regions and in the vicinity of airports,
The interpolation function works as expected: the interpolated wind deviates
from the large scale flow (trade winds) and tends to curve in the direction
indicated by wind barbs (see the areas highlighted with green arrow). Although,
in some areas, specially over complex terrain (central Colombia)  and Cuba, the interpolated wind is extremely
strong (see the areas highlighted with red arrow). It there is the possibility
I made a mistake in my code. However, I can’t find it. I also noted that
Cressman interpolation is very sensible to the rscan values. I’m attaching the
code. The NCL 6.5 version is used.</span></p>

<p class="MsoNormal" style="text-align:justify;line-height:12.65pt;background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial;margin:0in 0in 10pt;font-size:11pt;font-family:Calibri,sans-serif"><span style="font-size:12pt;font-family:"Times New Roman",serif">Any suggestion will be
greatly appreciated.</span></p>

<span style="font-size:12pt;line-height:115%;font-family:"Times New Roman",serif">Gerardo Montoya, full
professor (retired) at Universidad Nacional de Colombia </span>    <br></div>